diff --git a/core/includes/common.inc b/core/includes/common.inc
index 7bf85751200..79f16db246e 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -499,9 +499,9 @@ function _format_date_callback(array $matches = NULL, $new_langcode = NULL) {
  *   non-controller or sub-domain URIs such as core/install.php. Note that
  *   \Drupal\Core\Url::fromUri() expects a valid URI including the scheme. URIs
  *   from the same sub-domain that are not handled by Drupal controllers should
- *   be prepended with base://. For example:
+ *   use the base: scheme. For example:
  * @code
- * $installer_url = \Drupal\Core\Url::fromUri('base://core/install.php')->toString();
+ * $installer_url = \Drupal\Core\Url::fromUri('base:core/install.php')->toString();
  * $external_url = \Drupal\Core\Url::fromUri('http://example.com', ['query' => ['foo' => 'bar']])->toString();
  * $internal_url = \Drupal\Core\Url::fromRoute('system.admin')->toString();
  * @endcode
@@ -604,9 +604,9 @@ function drupal_http_header_attributes(array $attributes = array()) {
  *   core/install.php use \Drupal\Core\Url::fromUri(). Note that
  *   \Drupal\Core\Url::fromUri() expects a valid URI including the scheme. URIs
  *   from the same sub-domain that are not handled by Drupal controllers should
- *   be prepended with base://. For example:
+ *   be prepended with base:. For example:
  * @code
- * $installer_url = \Drupal\Core\Url::fromUri('base://core/install.php')->toString();
+ * $installer_url = \Drupal\Core\Url::fromUri('base:core/install.php')->toString();
  * $installer_link = \Drupal::l($text, $installer_url);
  * $external_url = \Drupal\Core\Url::fromUri('http://example.com', ['query' => ['foo' => 'bar']])->toString();
  * $external_link = \Drupal::l($text, $external_url);
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 06b62c5ef38..4191cdf0019 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -584,7 +584,7 @@ function install_run_task($task, &$install_state) {
       // Otherwise, the batch will complete.
       // Disable the default script for the URL and clone the object, as
       // batch_process() will add additional options to the batch URL.
-      $url = Url::fromUri('base://install.php', ['query' => $install_state['parameters'], 'script' => '']);
+      $url = Url::fromUri('base:install.php', ['query' => $install_state['parameters'], 'script' => '']);
       $response = batch_process($url, clone $url);
       if ($response instanceof Response) {
         // Save $_SESSION data from batch.
diff --git a/core/lib/Drupal.php b/core/lib/Drupal.php
index 7b52d13181d..34c641c0adf 100644
--- a/core/lib/Drupal.php
+++ b/core/lib/Drupal.php
@@ -476,7 +476,7 @@ class Drupal {
    * the \Drupal\Core\Url object. See \Drupal\Core\Url::fromRoute() for
    * detailed documentation. For non-routed local URIs relative to
    * the base path (like robots.txt) use Url::fromUri()->toString() with the
-   * base:// scheme.
+   * base: scheme.
    *
    * @param string $route_name
    *   The name of the route.
diff --git a/core/lib/Drupal/Core/Form/ConfirmFormHelper.php b/core/lib/Drupal/Core/Form/ConfirmFormHelper.php
index b58078d39e1..03c1c4092de 100644
--- a/core/lib/Drupal/Core/Form/ConfirmFormHelper.php
+++ b/core/lib/Drupal/Core/Form/ConfirmFormHelper.php
@@ -36,7 +36,7 @@ class ConfirmFormHelper {
       $options = UrlHelper::parse($query->get('destination'));
       // @todo Use Url::fromPath() once https://www.drupal.org/node/2351379 is
       //   resolved.
-      $url = Url::fromUri('base://' . $options['path'], $options);
+      $url = Url::fromUri('base:' . $options['path'], $options);
     }
     // Check for a route-based cancel link.
     else {
diff --git a/core/lib/Drupal/Core/Url.php b/core/lib/Drupal/Core/Url.php
index 8b43a5c79b2..560b7f49138 100644
--- a/core/lib/Drupal/Core/Url.php
+++ b/core/lib/Drupal/Core/Url.php
@@ -139,7 +139,7 @@ class Url {
    *
    * This method is for URLs that have Drupal routes (that is, most pages
    * generated by Drupal). For non-routed local URIs relative to the base
-   * path (like robots.txt) use Url::fromUri() with the base:// scheme.
+   * path (like robots.txt) use Url::fromUri() with the base: scheme.
    *
    * @param string $route_name
    *   The name of the route
@@ -193,7 +193,7 @@ class Url {
    *
    * This method is for generating URLs for URIs that:
    * - do not have Drupal routes: both external URLs and unrouted local URIs
-   *   like base://robots.txt
+   *   like base:robots.txt
    * - do have a Drupal route but have a custom scheme to simplify linking.
    *   Currently, there is only the entity: scheme (This allows URIs of the
    *   form entity:{entity_type}/{entity_id}. For example: entity:node/1
@@ -204,7 +204,7 @@ class Url {
    *
    * @param string $uri
    *   The URI of the resource including the scheme. For Drupal paths that are
-   *   not handled by the routing system, use base:// for the scheme. For entity
+   *   not handled by the routing system, use base: for the scheme. For entity
    *   URLs you may use entity:{entity_type}/{entity_id} URIs.
    * @param array $options
    *   (optional) An associative array of additional URL options, with the
@@ -233,15 +233,18 @@ class Url {
    */
   public static function fromUri($uri, $options = array()) {
     if (!($scheme = parse_url($uri, PHP_URL_SCHEME))) {
-      throw new \InvalidArgumentException(String::format('The URI "@uri" is invalid. You must use a valid URI scheme. Use base:// for a path, e.g., to a Drupal file that needs the base path. Do not use this for internal paths controlled by Drupal.', ['@uri' => $uri]));
+      throw new \InvalidArgumentException(String::format('The URI "@uri" is invalid. You must use a valid URI scheme. Use base: for a path, e.g., to a Drupal file that needs the base path. Do not use this for internal paths controlled by Drupal.', ['@uri' => $uri]));
     }
 
     // Special case entity: URIs. Map these to the canonical entity route.
     if ($scheme === 'entity') {
       return static::fromEntityUri($uri);
     }
-
     $url = new static($uri, array(), $options);
+    if ($scheme !== 'base') {
+      $url->external = TRUE;
+      $url->setOption('external', TRUE);
+    }
     $url->setUnrouted();
 
     return $url;
@@ -313,11 +316,6 @@ class Url {
     // Set empty route name and parameters.
     $this->routeName = NULL;
     $this->routeParameters = array();
-    // @todo Add a method for the check below in
-    // https://www.drupal.org/node/2346859.
-    if ($this->external = strpos($this->uri, 'base://') !== 0) {
-      $this->options['external'] = TRUE;
-    }
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Utility/UnroutedUrlAssembler.php b/core/lib/Drupal/Core/Utility/UnroutedUrlAssembler.php
index 612ac8754a1..bc21ea817c1 100644
--- a/core/lib/Drupal/Core/Utility/UnroutedUrlAssembler.php
+++ b/core/lib/Drupal/Core/Utility/UnroutedUrlAssembler.php
@@ -61,14 +61,14 @@ class UnroutedUrlAssembler implements UnroutedUrlAssemblerInterface {
     // Note that UrlHelper::isExternal will return FALSE if the $uri has a
     // disallowed protocol.  This is later made safe since we always add at
     // least a leading slash.
-    if (strpos($uri, 'base://') === 0) {
+    if (parse_url($uri, PHP_URL_SCHEME) === 'base') {
       return $this->buildLocalUrl($uri, $options);
     }
     elseif (UrlHelper::isExternal($uri)) {
       // UrlHelper::isExternal() only returns true for safe protocols.
       return $this->buildExternalUrl($uri, $options);
     }
-    throw new \InvalidArgumentException(String::format('The URI "@uri" is invalid. You must use a valid URI scheme. Use base:// for a path, e.g., to a Drupal file that needs the base path. Do not use this for internal paths controlled by Drupal.', ['@uri' => $uri]));
+    throw new \InvalidArgumentException(String::format('The URI "@uri" is invalid. You must use a valid URI scheme. Use base: for a path, e.g., to a Drupal file that needs the base path. Do not use this for internal paths controlled by Drupal.', ['@uri' => $uri]));
   }
 
   /**
@@ -108,8 +108,10 @@ class UnroutedUrlAssembler implements UnroutedUrlAssemblerInterface {
     $this->addOptionDefaults($options);
     $request = $this->requestStack->getCurrentRequest();
 
-    // Remove the base:// scheme.
-    $uri = substr($uri, 7);
+    // Remove the base: scheme.
+    // @todo Consider using a class constant for this in
+    //   https://www.drupal.org/node/2417459
+    $uri = substr($uri, 5);
 
     // Allow (outbound) path processing, if needed. A valid use case is the path
     // alias overview form:
diff --git a/core/lib/Drupal/Core/Utility/UnroutedUrlAssemblerInterface.php b/core/lib/Drupal/Core/Utility/UnroutedUrlAssemblerInterface.php
index d224a4799e5..868f0c171a4 100644
--- a/core/lib/Drupal/Core/Utility/UnroutedUrlAssemblerInterface.php
+++ b/core/lib/Drupal/Core/Utility/UnroutedUrlAssemblerInterface.php
@@ -18,11 +18,11 @@ interface UnroutedUrlAssemblerInterface {
    * domain-local URIs and external URLs.
    *
    * @param string $uri
-   *   A local URI or an external URL being linked to, such as "base://foo"
+   *   A local URI or an external URL being linked to, such as "base:foo"
    *    or "http://example.com/foo".
    *   - If you provide a full URL, it will be considered an external URL as
    *     long as it has an allowed protocol.
-   *   - If you provide only a local URI (e.g. "base://foo"), it will be
+   *   - If you provide only a local URI (e.g. "base:foo"), it will be
    *     considered a path local to Drupal, but not handled by the routing
    *     system.  The base path (the subdirectory where the front controller
    *     is found) will be added to the path. Additional query arguments for
diff --git a/core/modules/dblog/src/Controller/DbLogController.php b/core/modules/dblog/src/Controller/DbLogController.php
index e8b1ba5dc07..3470126d5b1 100644
--- a/core/modules/dblog/src/Controller/DbLogController.php
+++ b/core/modules/dblog/src/Controller/DbLogController.php
@@ -255,11 +255,11 @@ class DbLogController extends ControllerBase {
         ),
         array(
           array('data' => $this->t('Location'), 'header' => TRUE),
-          $this->l($dblog->location, $dblog->location ? Url::fromUri('base://' . $dblog->location) : Url::fromRoute('<none>')),
+          $this->l($dblog->location, $dblog->location ? Url::fromUri('base:' . $dblog->location) : Url::fromRoute('<none>')),
         ),
         array(
           array('data' => $this->t('Referrer'), 'header' => TRUE),
-          $this->l($dblog->referer, $dblog->referer ? Url::fromUri('base://' . $dblog->referer) : Url::fromRoute('<none>')),
+          $this->l($dblog->referer, $dblog->referer ? Url::fromUri('base:' . $dblog->referer) : Url::fromRoute('<none>')),
         ),
         array(
           array('data' => $this->t('Message'), 'header' => TRUE),
diff --git a/core/modules/field_ui/src/FieldUI.php b/core/modules/field_ui/src/FieldUI.php
index 4bbd93a9853..c6b33edb26f 100644
--- a/core/modules/field_ui/src/FieldUI.php
+++ b/core/modules/field_ui/src/FieldUI.php
@@ -63,7 +63,7 @@ class FieldUI {
       // Redirect to any given path within the same domain.
       // @todo Use Url::fromPath() once https://www.drupal.org/node/2351379 is
       //   resolved.
-      $next_destination = Url::fromUri('base://' . $options['path']);
+      $next_destination = Url::fromUri('base:' . $options['path']);
     }
     return $next_destination;
   }
diff --git a/core/modules/hal/src/Tests/DenormalizeTest.php b/core/modules/hal/src/Tests/DenormalizeTest.php
index cbb593c24aa..799585bc6d1 100644
--- a/core/modules/hal/src/Tests/DenormalizeTest.php
+++ b/core/modules/hal/src/Tests/DenormalizeTest.php
@@ -25,7 +25,7 @@ class DenormalizeTest extends NormalizerTestBase {
     $data_with_valid_type = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
         ),
       ),
     );
@@ -37,10 +37,10 @@ class DenormalizeTest extends NormalizerTestBase {
       '_links' => array(
         'type' => array(
           array(
-            'href' => Url::fromUri('base://rest/types/foo', array('absolute' => TRUE))->toString(),
+            'href' => Url::fromUri('base:rest/types/foo', array('absolute' => TRUE))->toString(),
           ),
           array(
-            'href' => Url::fromUri('base://rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
+            'href' => Url::fromUri('base:rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
           ),
         ),
       ),
@@ -52,7 +52,7 @@ class DenormalizeTest extends NormalizerTestBase {
     $data_with_invalid_type = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/types/foo', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/types/foo', array('absolute' => TRUE))->toString(),
         ),
       ),
     );
@@ -85,7 +85,7 @@ class DenormalizeTest extends NormalizerTestBase {
     $no_field_data = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
         ),
       ),
     );
@@ -95,7 +95,7 @@ class DenormalizeTest extends NormalizerTestBase {
     $empty_field_data = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
         ),
       ),
       'field_test_text' => array(),
@@ -113,7 +113,7 @@ class DenormalizeTest extends NormalizerTestBase {
     $data = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
         ),
       ),
       'uuid' => array(
@@ -183,7 +183,7 @@ class DenormalizeTest extends NormalizerTestBase {
     $data = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString(),
         ),
       ),
       'field_test_text' => array(
diff --git a/core/modules/hal/src/Tests/NormalizeTest.php b/core/modules/hal/src/Tests/NormalizeTest.php
index 183430fcb46..9525f056ca1 100644
--- a/core/modules/hal/src/Tests/NormalizeTest.php
+++ b/core/modules/hal/src/Tests/NormalizeTest.php
@@ -61,8 +61,8 @@ class NormalizeTest extends NormalizerTestBase {
     $entity->getTranslation('en')->set('field_test_entity_reference', array(0 => $translation_values['field_test_entity_reference']));
     $entity->save();
 
-    $type_uri = Url::fromUri('base://rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString();
-    $relation_uri = Url::fromUri('base://rest/relation/entity_test/entity_test/field_test_entity_reference', array('absolute' => TRUE))->toString();
+    $type_uri = Url::fromUri('base:rest/type/entity_test/entity_test', array('absolute' => TRUE))->toString();
+    $relation_uri = Url::fromUri('base:rest/relation/entity_test/entity_test/field_test_entity_reference', array('absolute' => TRUE))->toString();
 
     $expected_array = array(
       '_links' => array(
diff --git a/core/modules/image/src/Entity/ImageStyle.php b/core/modules/image/src/Entity/ImageStyle.php
index 624eea03b04..4c3775169b6 100644
--- a/core/modules/image/src/Entity/ImageStyle.php
+++ b/core/modules/image/src/Entity/ImageStyle.php
@@ -225,7 +225,7 @@ class ImageStyle extends ConfigEntityBase implements ImageStyleInterface, Entity
     // built.
     if ($clean_urls === FALSE && file_uri_scheme($uri) == 'public' && !file_exists($uri)) {
       $directory_path = file_stream_wrapper_get_instance_by_uri($uri)->getDirectoryPath();
-      return Url::fromUri('base://' . $directory_path . '/' . file_uri_target($uri), array('absolute' => TRUE, 'query' => $token_query))->toString();
+      return Url::fromUri('base:' . $directory_path . '/' . file_uri_target($uri), array('absolute' => TRUE, 'query' => $token_query))->toString();
     }
 
     $file_url = file_create_url($uri);
diff --git a/core/modules/image/src/Tests/ImageThemeFunctionTest.php b/core/modules/image/src/Tests/ImageThemeFunctionTest.php
index 2291b386db3..ad7af4dffc4 100644
--- a/core/modules/image/src/Tests/ImageThemeFunctionTest.php
+++ b/core/modules/image/src/Tests/ImageThemeFunctionTest.php
@@ -87,7 +87,7 @@ class ImageThemeFunctionTest extends WebTestBase {
       '#theme' => 'image_formatter',
       '#image_style' => 'test',
       '#item' => $entity->image_test,
-      '#url' => Url::fromUri('base://' . $path),
+      '#url' => Url::fromUri('base:' . $path),
     );
 
     // Test using theme_image_formatter() with a NULL value for the alt option.
diff --git a/core/modules/menu_ui/src/Tests/MenuTest.php b/core/modules/menu_ui/src/Tests/MenuTest.php
index 1f121ef64fa..a019bc91e54 100644
--- a/core/modules/menu_ui/src/Tests/MenuTest.php
+++ b/core/modules/menu_ui/src/Tests/MenuTest.php
@@ -116,7 +116,7 @@ class MenuTest extends MenuWebTestBase {
     // Verify delete link exists and reset link does not exist.
     $this->drupalGet('admin/structure/menu/manage/' . $this->menu->id());
     $this->assertLinkByHref('admin/structure/menu/item/' . $this->items[0]->id() . '/delete');
-    $this->assertNoLinkByHref(Url::fromUri('base://admin/structure/menu/link/' . $this->items[0]->getPluginId() . '/reset')->toString());
+    $this->assertNoLinkByHref(Url::fromUri('base:admin/structure/menu/link/' . $this->items[0]->getPluginId() . '/reset')->toString());
     // Check delete and reset access.
     $this->drupalGet('admin/structure/menu/item/' . $this->items[0]->id() . '/delete');
     $this->assertResponse(200);
diff --git a/core/modules/path/src/Controller/PathController.php b/core/modules/path/src/Controller/PathController.php
index 63b12f16792..f352de1419d 100644
--- a/core/modules/path/src/Controller/PathController.php
+++ b/core/modules/path/src/Controller/PathController.php
@@ -86,11 +86,11 @@ class PathController extends ControllerBase {
     $destination = drupal_get_destination();
     foreach ($this->aliasStorage->getAliasesForAdminListing($header, $keys) as $data) {
       $row = array();
-      $row['data']['alias'] = $this->l(Unicode::truncate($data->alias, 50, FALSE, TRUE), Url::fromUri('base://' . $data->source, array(
+      $row['data']['alias'] = $this->l(Unicode::truncate($data->alias, 50, FALSE, TRUE), Url::fromUri('base:' . $data->source, array(
         'path_processing' => TRUE,
         'attributes' => array('title' => $data->alias),
       )));
-      $row['data']['source'] = $this->l(Unicode::truncate($data->source, 50, FALSE, TRUE), Url::fromUri('base://' . $data->source, array(
+      $row['data']['source'] = $this->l(Unicode::truncate($data->source, 50, FALSE, TRUE), Url::fromUri('base:' . $data->source, array(
         'alias' => TRUE,
         'attributes' => array('title' => $data->source),
       )));
diff --git a/core/modules/rest/src/LinkManager/RelationLinkManager.php b/core/modules/rest/src/LinkManager/RelationLinkManager.php
index 54bec536ae3..38bf4cfcc85 100644
--- a/core/modules/rest/src/LinkManager/RelationLinkManager.php
+++ b/core/modules/rest/src/LinkManager/RelationLinkManager.php
@@ -54,7 +54,7 @@ class RelationLinkManager implements RelationLinkManagerInterface {
    * {@inheritdoc}
    */
   public function getRelationUri($entity_type, $bundle, $field_name) {
-    return $this->urlAssembler->assemble("base://rest/relation/$entity_type/$bundle/$field_name", array('absolute' => TRUE));
+    return $this->urlAssembler->assemble("base:rest/relation/$entity_type/$bundle/$field_name", array('absolute' => TRUE));
   }
 
   /**
diff --git a/core/modules/rest/src/LinkManager/TypeLinkManager.php b/core/modules/rest/src/LinkManager/TypeLinkManager.php
index 5a7e6034a7d..4160b2b4d78 100644
--- a/core/modules/rest/src/LinkManager/TypeLinkManager.php
+++ b/core/modules/rest/src/LinkManager/TypeLinkManager.php
@@ -53,7 +53,7 @@ class TypeLinkManager implements TypeLinkManagerInterface {
    */
   public function getTypeUri($entity_type, $bundle) {
     // @todo Make the base path configurable.
-    return $this->urlAssembler->assemble("base://rest/type/$entity_type/$bundle", array('absolute' => TRUE));
+    return $this->urlAssembler->assemble("base:rest/type/$entity_type/$bundle", array('absolute' => TRUE));
   }
 
   /**
diff --git a/core/modules/rest/src/Tests/NodeTest.php b/core/modules/rest/src/Tests/NodeTest.php
index 863cd0435ff..7169102eebd 100644
--- a/core/modules/rest/src/Tests/NodeTest.php
+++ b/core/modules/rest/src/Tests/NodeTest.php
@@ -70,7 +70,7 @@ class NodeTest extends RESTTestBase {
     $data = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/type/node/resttest', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/type/node/resttest', array('absolute' => TRUE))->toString(),
         ),
       ),
       'title' => array(
diff --git a/core/modules/serialization/src/Tests/EntityResolverTest.php b/core/modules/serialization/src/Tests/EntityResolverTest.php
index e87b69b8723..7d7c00d65a5 100644
--- a/core/modules/serialization/src/Tests/EntityResolverTest.php
+++ b/core/modules/serialization/src/Tests/EntityResolverTest.php
@@ -63,12 +63,12 @@ class EntityResolverTest extends NormalizerTestBase {
     $entity->set('field_test_entity_reference', array(array('target_id' => 1)));
     $entity->save();
 
-    $field_uri = Url::fromUri('base://rest/relation/entity_test_mulrev/entity_test_mulrev/field_test_entity_reference', array('absolute' => TRUE))->toString();
+    $field_uri = Url::fromUri('base:rest/relation/entity_test_mulrev/entity_test_mulrev/field_test_entity_reference', array('absolute' => TRUE))->toString();
 
     $data = array(
       '_links' => array(
         'type' => array(
-          'href' => Url::fromUri('base://rest/type/entity_test_mulrev/entity_test_mulrev', array('absolute' => TRUE))->toString(),
+          'href' => Url::fromUri('base:rest/type/entity_test_mulrev/entity_test_mulrev', array('absolute' => TRUE))->toString(),
         ),
         $field_uri => array(
           array(
diff --git a/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php b/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
index fedd64c0a88..e384a3c5a1f 100644
--- a/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
+++ b/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
@@ -77,7 +77,7 @@ class SimpleTestBrowserTest extends WebTestBase {
     // @see drupal_valid_test_ua()
     // Not using File API; a potential error must trigger a PHP warning.
     unlink($this->siteDirectory . '/.htkey');
-    $this->drupalGet(Url::fromUri('base://core/install.php', array('external' => TRUE, 'absolute' => TRUE))->toString());
+    $this->drupalGet(Url::fromUri('base:core/install.php', array('external' => TRUE, 'absolute' => TRUE))->toString());
     $this->assertResponse(403, 'Cannot access install.php.');
   }
 
diff --git a/core/modules/statistics/statistics.module b/core/modules/statistics/statistics.module
index c70c1a63f70..5d84cb9f307 100644
--- a/core/modules/statistics/statistics.module
+++ b/core/modules/statistics/statistics.module
@@ -40,7 +40,7 @@ function statistics_help($route_name, RouteMatchInterface $route_match) {
 function statistics_node_view(array &$build, EntityInterface $node, EntityViewDisplayInterface $display, $view_mode) {
   if (!$node->isNew() && $view_mode == 'full' && node_is_page($node) && empty($node->in_preview)) {
     $build['statistics_content_counter']['#attached']['library'][] = 'statistics/drupal.statistics';
-    $settings = array('data' => array('nid' => $node->id()), 'url' => Url::fromUri('base://' . drupal_get_path('module', 'statistics') . '/statistics.php')->toString());
+    $settings = array('data' => array('nid' => $node->id()), 'url' => Url::fromUri('base:' . drupal_get_path('module', 'statistics') . '/statistics.php')->toString());
     $build['statistics_content_counter']['#attached']['drupalSettings']['statistics'] = $settings;
   }
 }
diff --git a/core/modules/system/src/Tests/Common/AddFeedTest.php b/core/modules/system/src/Tests/Common/AddFeedTest.php
index 4fe5e6f388f..75a20d01f06 100644
--- a/core/modules/system/src/Tests/Common/AddFeedTest.php
+++ b/core/modules/system/src/Tests/Common/AddFeedTest.php
@@ -23,15 +23,15 @@ class AddFeedTest extends WebTestBase {
   function testBasicFeedAddNoTitle() {
     $path = $this->randomMachineName(12);
     $external_url = 'http://' . $this->randomMachineName(12) . '/' . $this->randomMachineName(12);
-    $fully_qualified_local_url = Url::fromUri('base://' . $this->randomMachineName(12), array('absolute' => TRUE))->toString();
+    $fully_qualified_local_url = Url::fromUri('base:' . $this->randomMachineName(12), array('absolute' => TRUE))->toString();
 
     $path_for_title = $this->randomMachineName(12);
     $external_for_title = 'http://' . $this->randomMachineName(12) . '/' . $this->randomMachineName(12);
-    $fully_qualified_for_title = Url::fromUri('base://' . $this->randomMachineName(12), array('absolute' => TRUE))->toString();
+    $fully_qualified_for_title = Url::fromUri('base:' . $this->randomMachineName(12), array('absolute' => TRUE))->toString();
 
     $urls = array(
       'path without title' => array(
-        'url' => Url::fromUri('base://' . $path, array('absolute' => TRUE))->toString(),
+        'url' => Url::fromUri('base:' . $path, array('absolute' => TRUE))->toString(),
         'title' => '',
       ),
       'external URL without title' => array(
@@ -43,7 +43,7 @@ class AddFeedTest extends WebTestBase {
         'title' => '',
       ),
       'path with title' => array(
-        'url' => Url::fromUri('base://' . $path_for_title, array('absolute' => TRUE))->toString(),
+        'url' => Url::fromUri('base:' . $path_for_title, array('absolute' => TRUE))->toString(),
         'title' => $this->randomMachineName(12),
       ),
       'external URL with title' => array(
diff --git a/core/modules/system/src/Tests/Common/UrlTest.php b/core/modules/system/src/Tests/Common/UrlTest.php
index 21ea4322196..eb61b06a171 100644
--- a/core/modules/system/src/Tests/Common/UrlTest.php
+++ b/core/modules/system/src/Tests/Common/UrlTest.php
@@ -32,12 +32,12 @@ class UrlTest extends WebTestBase {
     $text = $this->randomMachineName();
     $path = "<SCRIPT>alert('XSS')</SCRIPT>";
     $link = _l($text, $path);
-    $sanitized_path = check_url(Url::fromUri('base://' . $path)->toString());
+    $sanitized_path = check_url(Url::fromUri('base:' . $path)->toString());
     $this->assertTrue(strpos($link, $sanitized_path) !== FALSE, format_string('XSS attack @path was filtered by _l().', array('@path' => $path)));
 
     // Test \Drupal\Core\Url.
-    $link = Url::fromUri('base://' . $path)->toString();
-    $sanitized_path = check_url(Url::fromUri('base://' . $path)->toString());
+    $link = Url::fromUri('base:' . $path)->toString();
+    $sanitized_path = check_url(Url::fromUri('base:' . $path)->toString());
     $this->assertTrue(strpos($link, $sanitized_path) !== FALSE, format_string('XSS attack @path was filtered by #theme', ['@path' => $path]));
   }
 
diff --git a/core/modules/system/src/Tests/Menu/AssertBreadcrumbTrait.php b/core/modules/system/src/Tests/Menu/AssertBreadcrumbTrait.php
index 463ad4e17fc..a9d421aa755 100644
--- a/core/modules/system/src/Tests/Menu/AssertBreadcrumbTrait.php
+++ b/core/modules/system/src/Tests/Menu/AssertBreadcrumbTrait.php
@@ -71,13 +71,13 @@ trait AssertBreadcrumbTrait {
       foreach ($trail as $path => $title) {
         // If the path is empty, generate the path from the <front> route.  If
         // the path does not start with a leading, then run it through
-        // Url::fromUri('base://')->toString() to get correct the base
+        // Url::fromUri('base:')->toString() to get correct the base
         // prepended.
         if ($path == '') {
           $url = Url::fromRoute('<front>')->toString();
         }
         elseif ($path[0] != '/') {
-          $url = Url::fromUri('base://' . $path)->toString();
+          $url = Url::fromUri('base:' . $path)->toString();
         }
         else {
           $url = $path;
diff --git a/core/modules/system/src/Tests/Menu/AssertMenuActiveTrailTrait.php b/core/modules/system/src/Tests/Menu/AssertMenuActiveTrailTrait.php
index ecf6f4368a0..d217c6640bf 100644
--- a/core/modules/system/src/Tests/Menu/AssertMenuActiveTrailTrait.php
+++ b/core/modules/system/src/Tests/Menu/AssertMenuActiveTrailTrait.php
@@ -37,7 +37,7 @@ trait AssertMenuActiveTrailTrait {
         $part_xpath .= 'li[contains(@class, :class)]/a[contains(@href, :href) and contains(text(), :title)]';
         $part_args = array(
           ':class' => 'active-trail',
-          ':href' => Url::fromUri('base://' . $link_path)->toString(),
+          ':href' => Url::fromUri('base:' . $link_path)->toString(),
           ':title' => $link_title,
         );
         $xpath .= $this->buildXPathQuery($part_xpath, $part_args);
@@ -57,7 +57,7 @@ trait AssertMenuActiveTrailTrait {
     $args = array(
       ':class-trail' => 'active-trail',
       ':class-active' => 'active',
-      ':href' => Url::fromUri('base://' . $active_link_path)->toString(),
+      ':href' => Url::fromUri('base:' . $active_link_path)->toString(),
       ':title' => $active_link_title,
     );
     $elements = $this->xpath($xpath, $args);
diff --git a/core/modules/system/src/Tests/Menu/BreadcrumbTest.php b/core/modules/system/src/Tests/Menu/BreadcrumbTest.php
index f1dc18efa69..ed4d35ab949 100644
--- a/core/modules/system/src/Tests/Menu/BreadcrumbTest.php
+++ b/core/modules/system/src/Tests/Menu/BreadcrumbTest.php
@@ -278,7 +278,7 @@ class BreadcrumbTest extends MenuTestBase {
       // other than the breadcrumb trail.
       $elements = $this->xpath('//nav[@id=:menu]/descendant::a[@href=:href]', array(
         ':menu' => 'block-bartik-tools',
-        ':href' => Url::fromUri('base://' . $link_path)->toString(),
+        ':href' => Url::fromUri('base:' . $link_path)->toString(),
       ));
       $this->assertTrue(count($elements) == 1, "Link to {$link_path} appears only once.");
 
diff --git a/core/modules/system/src/Tests/Menu/LocalTasksTest.php b/core/modules/system/src/Tests/Menu/LocalTasksTest.php
index 37b44d8aad5..ea376d65109 100644
--- a/core/modules/system/src/Tests/Menu/LocalTasksTest.php
+++ b/core/modules/system/src/Tests/Menu/LocalTasksTest.php
@@ -35,7 +35,7 @@ class LocalTasksTest extends WebTestBase {
     ));
     $this->assertTrue(count($elements), 'Local tasks found.');
     foreach ($hrefs as $index => $element) {
-      $expected = Url::fromUri('base://' . $hrefs[$index])->toString();
+      $expected = Url::fromUri('base:' . $hrefs[$index])->toString();
       $method = ($elements[$index]['href'] == $expected ? 'pass' : 'fail');
       $this->{$method}(format_string('Task @number href @value equals @expected.', array(
         '@number' => $index + 1,
diff --git a/core/modules/system/src/Tests/Theme/FunctionsTest.php b/core/modules/system/src/Tests/Theme/FunctionsTest.php
index abdcff646ff..a96b8e42bf1 100644
--- a/core/modules/system/src/Tests/Theme/FunctionsTest.php
+++ b/core/modules/system/src/Tests/Theme/FunctionsTest.php
@@ -191,7 +191,7 @@ class FunctionsTest extends WebTestBase {
     $variables['links'] = array(
       'a link' => array(
         'title' => 'A <link>',
-        'url' => Url::fromUri('base://a/link'),
+        'url' => Url::fromUri('base:a/link'),
       ),
       'plain text' => array(
         'title' => 'Plain "text"',
@@ -215,7 +215,7 @@ class FunctionsTest extends WebTestBase {
 
     $expected_links = '';
     $expected_links .= '<ul id="somelinks">';
-    $expected_links .= '<li class="a-link"><a href="' . Url::fromUri('base://a/link')->toString() . '">' . String::checkPlain('A <link>') . '</a></li>';
+    $expected_links .= '<li class="a-link"><a href="' . Url::fromUri('base:a/link')->toString() . '">' . String::checkPlain('A <link>') . '</a></li>';
     $expected_links .= '<li class="plain-text">' . String::checkPlain('Plain "text"') . '</li>';
     $expected_links .= '<li class="front-page"><a href="' . Url::fromRoute('<front>')->toString() . '">' . String::checkPlain('Front page') . '</a></li>';
     $expected_links .= '<li class="router-test"><a href="' . \Drupal::urlGenerator()->generate('router_test.1') . '">' . String::checkPlain('Test route') . '</a></li>';
@@ -254,7 +254,7 @@ class FunctionsTest extends WebTestBase {
     );
     $expected_links = '';
     $expected_links .= '<ul id="somelinks">';
-    $expected_links .= '<li class="a-link"><a href="' . Url::fromUri('base://a/link')->toString() . '">' . String::checkPlain('A <link>') . '</a></li>';
+    $expected_links .= '<li class="a-link"><a href="' . Url::fromUri('base:a/link')->toString() . '">' . String::checkPlain('A <link>') . '</a></li>';
     $expected_links .= '<li class="plain-text"><span class="a/class">' . String::checkPlain('Plain "text"') . '</span></li>';
     $expected_links .= '<li class="front-page"><a href="' . Url::fromRoute('<front>')->toString() . '">' . String::checkPlain('Front page') . '</a></li>';
     $expected_links .= '<li class="router-test"><a href="' . \Drupal::urlGenerator()->generate('router_test.1') . '">' . String::checkPlain('Test route') . '</a></li>';
@@ -269,7 +269,7 @@ class FunctionsTest extends WebTestBase {
     $variables['set_active_class'] = TRUE;
     $expected_links = '';
     $expected_links .= '<ul id="somelinks">';
-    $expected_links .= '<li class="a-link"><a href="' . Url::fromUri('base://a/link')->toString() . '">' . String::checkPlain('A <link>') . '</a></li>';
+    $expected_links .= '<li class="a-link"><a href="' . Url::fromUri('base:a/link')->toString() . '">' . String::checkPlain('A <link>') . '</a></li>';
     $expected_links .= '<li class="plain-text"><span class="a/class">' . String::checkPlain('Plain "text"') . '</span></li>';
     $expected_links .= '<li data-drupal-link-system-path="&lt;front&gt;" class="front-page"><a href="' . Url::fromRoute('<front>')->toString() . '" data-drupal-link-system-path="&lt;front&gt;">' . String::checkPlain('Front page') . '</a></li>';
     $expected_links .= '<li data-drupal-link-system-path="router_test/test1" class="router-test"><a href="' . \Drupal::urlGenerator()->generate('router_test.1') . '" data-drupal-link-system-path="router_test/test1">' . String::checkPlain('Test route') . '</a></li>';
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 0ce6b42ceda..e198431dbb1 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -421,7 +421,7 @@ function system_authorized_init($callback, $file, $arguments = array(), $page_ti
 function system_authorized_get_url(array $options = array()) {
   global $base_url;
   // Prefix with $base_url so url() treats it as an external link.
-  $url = Url::fromUri('base://core/authorize.php');
+  $url = Url::fromUri('base:core/authorize.php');
   $url_options = $url->getOptions();
   $url->setOptions($options + $url_options);
   return $url;
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php
index 925c84e32d4..cccdb37e727 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php
@@ -56,7 +56,7 @@ class FormTestRedirectForm extends FormBase {
       if (!$form_state->isValueEmpty('destination')) {
         // @todo Use Url::fromPath() once https://www.drupal.org/node/2351379 is
         //   resolved.
-        $form_state->setRedirectUrl(Url::fromUri('base://' . $form_state->getValue('destination')));
+        $form_state->setRedirectUrl(Url::fromUri('base:' . $form_state->getValue('destination')));
       }
     }
     else {
diff --git a/core/modules/update/src/Tests/UpdateTestBase.php b/core/modules/update/src/Tests/UpdateTestBase.php
index 52060701146..3d36aac2498 100644
--- a/core/modules/update/src/Tests/UpdateTestBase.php
+++ b/core/modules/update/src/Tests/UpdateTestBase.php
@@ -44,7 +44,7 @@ abstract class UpdateTestBase extends WebTestBase {
   protected function refreshUpdateStatus($xml_map, $url = 'update-test') {
     // Tell the Update Manager module to fetch from the URL provided by
     // update_test module.
-    $this->config('update.settings')->set('fetch.url', Url::fromUri('base://' . $url, array('absolute' => TRUE))->toString())->save();
+    $this->config('update.settings')->set('fetch.url', Url::fromUri('base:' . $url, array('absolute' => TRUE))->toString())->save();
     // Save the map for UpdateTestController::updateTest() to use.
     $this->config('update_test.settings')->set('xml_map', $xml_map)->save();
     // Manually check the update status.
diff --git a/core/modules/views/src/Plugin/views/display/PathPluginBase.php b/core/modules/views/src/Plugin/views/display/PathPluginBase.php
index 4503d0aa5da..77389336071 100644
--- a/core/modules/views/src/Plugin/views/display/PathPluginBase.php
+++ b/core/modules/views/src/Plugin/views/display/PathPluginBase.php
@@ -458,7 +458,7 @@ abstract class PathPluginBase extends DisplayPluginBase implements DisplayRouter
       $errors[] = $this->t('No query allowed.');
     }
 
-    if (!parse_url('base://' . $path)) {
+    if (!parse_url('base:' . $path)) {
       $errors[] = $this->t('Invalid path. Valid characters are alphanumerics as well as "-", ".", "_" and "~".');
     }
 
diff --git a/core/modules/views/src/Plugin/views/field/Links.php b/core/modules/views/src/Plugin/views/field/Links.php
index cf06b629502..4e2c73abf26 100644
--- a/core/modules/views/src/Plugin/views/field/Links.php
+++ b/core/modules/views/src/Plugin/views/field/Links.php
@@ -85,7 +85,7 @@ abstract class Links extends FieldPluginBase {
       $path = strip_tags(String::decodeEntities($this->viewsTokenReplace($path, $tokens)));
 
       $links[$field] = array(
-        'url' => $path ? UrlObject::fromUri('base://' . $path) : $url,
+        'url' => $path ? UrlObject::fromUri('base:' . $path) : $url,
         'title' => $title,
       );
       if (!empty($this->options['destination'])) {
diff --git a/core/modules/views/src/Tests/Handler/FieldUrlTest.php b/core/modules/views/src/Tests/Handler/FieldUrlTest.php
index fe6d71af308..67616caae2a 100644
--- a/core/modules/views/src/Tests/Handler/FieldUrlTest.php
+++ b/core/modules/views/src/Tests/Handler/FieldUrlTest.php
@@ -71,7 +71,7 @@ class FieldUrlTest extends ViewUnitTestBase {
 
     $this->executeView($view);
 
-    $this->assertEqual(\Drupal::l('John', Url::fromUri('base://John')), $view->field['name']->advancedRender($view->result[0]));
+    $this->assertEqual(\Drupal::l('John', Url::fromUri('base:John')), $view->field['name']->advancedRender($view->result[0]));
   }
 
 }
diff --git a/core/modules/views/src/Tests/Wizard/MenuTest.php b/core/modules/views/src/Tests/Wizard/MenuTest.php
index 63a325c2477..6f29329a057 100644
--- a/core/modules/views/src/Tests/Wizard/MenuTest.php
+++ b/core/modules/views/src/Tests/Wizard/MenuTest.php
@@ -41,7 +41,7 @@ class MenuTest extends WizardTestBase {
     $this->drupalGet('');
     $this->assertResponse(200);
     $this->assertLink($view['page[link_properties][title]']);
-    $this->assertLinkByHref(Url::fromUri('base://' . $view['page[path]'])->toString());
+    $this->assertLinkByHref(Url::fromUri('base:' . $view['page[path]'])->toString());
 
     // Make sure the link is associated with the main menu.
     /** @var \Drupal\Core\Menu\MenuLinkManagerInterface $menu_link_manager */
diff --git a/core/modules/views_ui/src/Tests/DefaultViewsTest.php b/core/modules/views_ui/src/Tests/DefaultViewsTest.php
index 68e298c6ad6..44af3a17f50 100644
--- a/core/modules/views_ui/src/Tests/DefaultViewsTest.php
+++ b/core/modules/views_ui/src/Tests/DefaultViewsTest.php
@@ -170,7 +170,7 @@ class DefaultViewsTest extends UITestBase {
 
     // Check that a dynamic path is shown as text.
     $this->assertRaw('test_route_with_suffix/%/suffix');
-    $this->assertNoLinkByHref(Url::fromUri('base://test_route_with_suffix/%/suffix')->toString());
+    $this->assertNoLinkByHref(Url::fromUri('base:test_route_with_suffix/%/suffix')->toString());
   }
 
   /**
diff --git a/core/modules/views_ui/src/Tests/DisplayPathTest.php b/core/modules/views_ui/src/Tests/DisplayPathTest.php
index 71b203541df..5b2a02284e1 100644
--- a/core/modules/views_ui/src/Tests/DisplayPathTest.php
+++ b/core/modules/views_ui/src/Tests/DisplayPathTest.php
@@ -105,10 +105,6 @@ class DisplayPathTest extends UITestBase {
     $this->drupalPostForm('admin/structure/views/nojs/display/test_view/page_1/path', array('path' => '?bar'), t('Apply'));
     $this->assertText('Path is empty');
 
-    // Add an invalid path from a random test failure.
-    $this->drupalPostForm('admin/structure/views/nojs/display/test_view/page_1/path', array('path' => 'AKI@&hO@'), t('Apply'));
-    $this->assertText('Invalid path');
-
     // Provide a random, valid path string.
     $random_string = $this->randomMachineName();
 
diff --git a/core/modules/views_ui/src/ViewEditForm.php b/core/modules/views_ui/src/ViewEditForm.php
index 59432172713..363474dd47e 100644
--- a/core/modules/views_ui/src/ViewEditForm.php
+++ b/core/modules/views_ui/src/ViewEditForm.php
@@ -318,7 +318,7 @@ class ViewEditForm extends ViewFormBase {
       }
       // @todo Use Url::fromPath() once https://www.drupal.org/node/2351379 is
       //   resolved.
-      $form_state->setRedirectUrl(Url::fromUri("base://$destination"));
+      $form_state->setRedirectUrl(Url::fromUri("base:$destination"));
     }
 
     $view->save();
@@ -424,7 +424,7 @@ class ViewEditForm extends ViewFormBase {
               '#options' => array('alt' => array($this->t("Go to the real page for this display"))),
               // @todo Use Url::fromPath() once
               //   https://www.drupal.org/node/2351379 is resolved.
-              '#url' => Url::fromUri("base://$path"),
+              '#url' => Url::fromUri("base:$path"),
               '#prefix' => '<li class="view">',
               "#suffix" => '</li>',
             );
diff --git a/core/modules/views_ui/src/ViewListBuilder.php b/core/modules/views_ui/src/ViewListBuilder.php
index f9ac0e1a570..39610436967 100644
--- a/core/modules/views_ui/src/ViewListBuilder.php
+++ b/core/modules/views_ui/src/ViewListBuilder.php
@@ -263,7 +263,7 @@ class ViewListBuilder extends ConfigEntityListBuilder {
       if ($display->hasPath()) {
         $path = $display->getPath();
         if ($view->status() && strpos($path, '%') === FALSE) {
-          $all_paths[] = \Drupal::l('/' . $path, Url::fromUri('base://' . $path));
+          $all_paths[] = \Drupal::l('/' . $path, Url::fromUri('base:' . $path));
         }
         else {
           $all_paths[] = String::checkPlain('/' . $path);
diff --git a/core/modules/views_ui/src/ViewUI.php b/core/modules/views_ui/src/ViewUI.php
index 70241ef6919..2153058f190 100644
--- a/core/modules/views_ui/src/ViewUI.php
+++ b/core/modules/views_ui/src/ViewUI.php
@@ -702,7 +702,7 @@ class ViewUI implements ViewEntityInterface {
               Xss::filterAdmin($this->executable->getTitle()),
             );
             if (isset($path)) {
-              $path = \Drupal::l($path, Url::fromUri('base://' . $path));
+              $path = \Drupal::l($path, Url::fromUri('base:' . $path));
             }
             else {
               $path = t('This display has no path.');
diff --git a/core/tests/Drupal/Tests/Core/Form/ConfirmFormHelperTest.php b/core/tests/Drupal/Tests/Core/Form/ConfirmFormHelperTest.php
index b80567fff50..540046a21f2 100644
--- a/core/tests/Drupal/Tests/Core/Form/ConfirmFormHelperTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/ConfirmFormHelperTest.php
@@ -96,7 +96,7 @@ class ConfirmFormHelperTest extends UnitTestCase {
     $query = array('destination' => 'baz');
     $form = $this->getMock('Drupal\Core\Form\ConfirmFormInterface');
     $link = ConfirmFormHelper::buildCancelLink($form, new Request($query));
-    $this->assertSame('base://' . $query['destination'], $link['#url']->getUri());
+    $this->assertSame('base:' . $query['destination'], $link['#url']->getUri());
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php b/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php
index d07e07b1b21..f237422984e 100644
--- a/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php
+++ b/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php
@@ -45,7 +45,7 @@ class UnroutedUrlTest extends UnitTestCase {
    *
    * @var string
    */
-  protected $unroutedInternal = 'base://robots.txt';
+  protected $unroutedInternal = 'base:robots.txt';
 
   /**
    * {@inheritdoc}
@@ -69,20 +69,53 @@ class UnroutedUrlTest extends UnitTestCase {
    * Tests the fromUri() method.
    *
    * @covers ::fromUri
+   *
+   * @dataProvider providerFromUri
    */
-  public function testFromUri() {
-    $urls = [
-      Url::fromUri($this->unroutedExternal),
-      Url::fromUri($this->unroutedInternal)
+  public function testFromUri($uri, $is_external) {
+    $url = Url::fromUri($uri);
+
+    $this->assertInstanceOf('Drupal\Core\Url', $url);
+  }
+
+
+  /**
+   * Data provider for testFromUri().
+   */
+  public function providerFromUri() {
+    return [
+      ['http://drupal.org', TRUE],
+      ['base:robots.txt', FALSE],
+      ['base:AKI@&hO@', FALSE],
+      ['base:(:;2&+h^', FALSE],
     ];
+  }
 
-    $this->assertInstanceOf('Drupal\Core\Url', $urls[0]);
-    $this->assertTrue($urls[0]->isExternal());
+  /**
+   * Tests the fromUri() method.
+   *
+   * @covers ::fromUri
+   * @dataProvider providerFromInvalidUri
+   * @expectedException \InvalidArgumentException
+   */
+  public function testFromInvalidUri($uri) {
+    $url = Url::fromUri($uri);
+  }
 
-    $this->assertInstanceOf('Drupal\Core\Url', $urls[1]);
-    $this->assertFalse($urls[1]->isExternal());
-
-    return $urls;
+  /**
+   * Data provider for testFromInvalidUri().
+   */
+  public function providerFromInvalidUri() {
+    return [
+      ['base://AKI@&hO@'],
+      ['#foo'],
+      ['foo?bar'],
+      ['?bar'],
+      ['base://(:;2&+h^'],
+      ['test'],
+      ['/test'],
+      ['//test'],
+    ];
   }
 
   /**
@@ -103,102 +136,101 @@ class UnroutedUrlTest extends UnitTestCase {
     $this->assertNull(Url::createFromRequest($request));
   }
 
-  /**
-   * Tests the fromUri() method with an non-scheme path.
-   *
-   * @covers ::fromUri
-   *
-   * @expectedException \InvalidArgumentException
-   */
-  public function testFromUriWithNonScheme() {
-    Url::fromUri('test');
-  }
-
   /**
    * Tests the isExternal() method.
    *
    * @depends testFromUri
+   * @dataProvider providerFromUri
    *
    * @covers ::isExternal
    */
-  public function testIsExternal(array $urls) {
-    $this->assertTrue($urls[0]->isExternal());
-    $this->assertFalse($urls[1]->isExternal());
+  public function testIsExternal($uri, $is_external) {
+    $url = Url::fromUri($uri);
+    $this->assertSame($url->isExternal(), $is_external);
   }
 
   /**
    * Tests the toString() method.
    *
    * @depends testFromUri
+   * @dataProvider providerFromUri
    *
    * @covers ::toString
    */
-  public function testToString(array $urls) {
-    $this->assertSame($this->unroutedExternal, $urls[0]->toString());
-    $this->assertSame($this->unroutedInternal, $urls[1]->toString());
+  public function testToString($uri) {
+    $url = Url::fromUri($uri);
+    $this->assertSame($uri, $url->toString());
   }
 
   /**
    * Tests the getRouteName() method.
    *
    * @depends testFromUri
+   * @dataProvider providerFromUri
    *
    * @expectedException \UnexpectedValueException
    *
    * @covers ::getRouteName
    */
-  public function testGetRouteName(array $urls) {
-    $urls[0]->getRouteName();
+  public function testGetRouteName($uri) {
+    $url = Url::fromUri($uri);
+    $url->getRouteName();
   }
 
   /**
    * Tests the getRouteParameters() method.
    *
    * @depends testFromUri
+   * @dataProvider providerFromUri
    *
    * @expectedException \UnexpectedValueException
    *
    * @covers ::getRouteParameters
    */
-  public function testGetRouteParameters(array $urls) {
-    $urls[0]->getRouteParameters();
+  public function testGetRouteParameters($uri) {
+    $url = Url::fromUri($uri);
+    $url->getRouteParameters();
   }
 
   /**
    * Tests the getInternalPath() method.
    *
    * @depends testFromUri
+   * @dataProvider providerFromUri
    *
    * @covers ::getInternalPath
    *
    * @expectedException \Exception
    */
-  public function testGetInternalPath(array $urls) {
-    $this->assertNull($urls[0]->getInternalPath());
+  public function testGetInternalPath($uri) {
+    $url = Url::fromUri($uri);
+    $this->assertNull($url->getInternalPath());
   }
 
   /**
    * Tests the getPath() method.
    *
    * @depends testFromUri
+   * @dataProvider providerFromUri
    *
    * @covers ::getUri
    */
-  public function testGetUri(array $urls) {
-    $this->assertNotNull($urls[0]->getUri());
-    $this->assertNotNull($urls[1]->getUri());
+  public function testGetUri($uri) {
+    $url = Url::fromUri($uri);
+    $this->assertNotNull($url->getUri());
   }
 
   /**
    * Tests the getOptions() method.
    *
    * @depends testFromUri
+   * @dataProvider providerFromUri
    *
    * @covers ::getOptions
    */
-  public function testGetOptions(array $urls) {
-    $this->assertInternalType('array', $urls[0]->getOptions());
-    $this->assertInternalType('array', $urls[1]->getOptions());
+  public function testGetOptions($uri) {
+    $url = Url::fromUri($uri);
+    $this->assertInternalType('array', $url->getOptions());
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Utility/UnroutedUrlAssemblerTest.php b/core/tests/Drupal/Tests/Core/Utility/UnroutedUrlAssemblerTest.php
index 7bd4836c8f7..b6253f00331 100644
--- a/core/tests/Drupal/Tests/Core/Utility/UnroutedUrlAssemblerTest.php
+++ b/core/tests/Drupal/Tests/Core/Utility/UnroutedUrlAssemblerTest.php
@@ -109,12 +109,12 @@ class UnroutedUrlAssemblerTest extends UnitTestCase {
    */
   public function providerTestAssembleWithLocalUri() {
     return [
-      ['base://example', [], FALSE, '/example'],
-      ['base://example', ['query' => ['foo' => 'bar']], FALSE, '/example?foo=bar'],
-      ['base://example', ['fragment' => 'example', ], FALSE, '/example#example'],
-      ['base://example', [], TRUE, '/subdir/example'],
-      ['base://example', ['query' => ['foo' => 'bar']], TRUE, '/subdir/example?foo=bar'],
-      ['base://example', ['fragment' => 'example', ], TRUE, '/subdir/example#example'],
+      ['base:example', [], FALSE, '/example'],
+      ['base:example', ['query' => ['foo' => 'bar']], FALSE, '/example?foo=bar'],
+      ['base:example', ['fragment' => 'example', ], FALSE, '/example#example'],
+      ['base:example', [], TRUE, '/subdir/example'],
+      ['base:example', ['query' => ['foo' => 'bar']], TRUE, '/subdir/example?foo=bar'],
+      ['base:example', ['fragment' => 'example', ], TRUE, '/subdir/example#example'],
     ];
   }
 
@@ -125,7 +125,7 @@ class UnroutedUrlAssemblerTest extends UnitTestCase {
     $this->setupRequestStack(FALSE);
     $this->pathProcessor->expects($this->never())
       ->method('processOutbound');
-    $result = $this->unroutedUrlAssembler->assemble('base://test-uri', []);
+    $result = $this->unroutedUrlAssembler->assemble('base:test-uri', []);
     $this->assertEquals('/test-uri', $result);
   }
 
@@ -138,7 +138,7 @@ class UnroutedUrlAssemblerTest extends UnitTestCase {
       ->method('processOutbound')
       ->with('test-uri', ['path_processing' => TRUE, 'fragment' => NULL, 'query' => [], 'absolute' => NULL, 'prefix' => NULL, 'script' => NULL])
       ->willReturn('test-other-uri');
-    $result = $this->unroutedUrlAssembler->assemble('base://test-uri', ['path_processing' => TRUE]);
+    $result = $this->unroutedUrlAssembler->assemble('base:test-uri', ['path_processing' => TRUE]);
     $this->assertEquals('/test-other-uri', $result);
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php b/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php
index af343940ddd..e12189fd357 100644
--- a/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php
+++ b/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php
@@ -71,8 +71,8 @@ class PrimitiveTypeConstraintValidatorTest extends UnitTestCase {
     $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'https://www.drupal.org', TRUE];
     $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'Invalid', FALSE];
     $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'entity:node/1', TRUE];
-    $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'base://', FALSE];
-    $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'base://node', TRUE];
+    $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'base:', TRUE];
+    $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'base:node', TRUE];
     $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'user-path:', TRUE];
     $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'public://', FALSE];
     $data[] = [$this->getMock('Drupal\Core\TypedData\Type\UriInterface'), 'public://foo.png', TRUE];