diff --git a/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php b/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php
index 13cdf21..c54e3f6 100644
--- a/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php
@@ -44,17 +44,9 @@ public static function getType() {
    *
    * @return string
    *   The extension name.
-   *
-   * @throws \InvalidArgumentException
-   *   In case of a malformed uri.
    */
   protected function getOwnerName() {
     $uri_parts = explode('://', $this->uri, 2);
-    if (count($uri_parts) === 1) {
-      // The delimiter ('://') was not found in $uri, malformed $uri passed.
-      throw new \InvalidArgumentException("Malformed uri parameter passed: {$this->uri}");
-    }
-
     // Remove the trailing filename from the path.
     $length = strpos($uri_parts[1], '/');
     return ($length === FALSE) ? $uri_parts[1] : substr($uri_parts[1], 0, $length);
diff --git a/core/lib/Drupal/Core/StreamWrapper/LocalStream.php b/core/lib/Drupal/Core/StreamWrapper/LocalStream.php
index 87c2ce2..fed91b0 100644
--- a/core/lib/Drupal/Core/StreamWrapper/LocalStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/LocalStream.php
@@ -18,34 +18,11 @@
  * \Drupal\Core\StreamWrapper\LocalStream implementations need to implement at
  * least the getDirectoryPath() and getExternalUrl() methods.
  */
-abstract class LocalStream implements StreamWrapperInterface {
+abstract class LocalStream extends StreamWrapperBase {
 
   use LocalStreamTrait;
 
   /**
-   * Stream context resource.
-   *
-   * @var resource
-   */
-  public $context;
-
-  /**
-   * A generic resource handle.
-   *
-   * @var resource
-   */
-  public $handle = NULL;
-
-  /**
-   * Instance URI (stream).
-   *
-   * A stream is referenced as "scheme://target".
-   *
-   * @var string
-   */
-  protected $uri;
-
-  /**
    * {@inheritdoc}
    */
   public static function getType() {
@@ -63,20 +40,6 @@ public static function getType() {
   /**
    * {@inheritdoc}
    */
-  function setUri($uri) {
-    $this->uri = $uri;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  function getUri() {
-    return $this->uri;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function realpath() {
     return $this->getLocalPath();
   }
diff --git a/core/lib/Drupal/Core/StreamWrapper/LocalStreamTrait.php b/core/lib/Drupal/Core/StreamWrapper/LocalStreamTrait.php
index 0fcc87e..871544a 100644
--- a/core/lib/Drupal/Core/StreamWrapper/LocalStreamTrait.php
+++ b/core/lib/Drupal/Core/StreamWrapper/LocalStreamTrait.php
@@ -7,6 +7,9 @@
 
 namespace Drupal\Core\StreamWrapper;
 
+/**
+ * Provides common methods for local streams.
+ */
 trait LocalStreamTrait {
 
   /**
diff --git a/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php b/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php
index cc6da4b..c0ca884 100644
--- a/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php
@@ -17,43 +17,7 @@
  * Drupal\Core\StreamWrapper\ReadOnlyStream implementations need to implement
  * all the read-related classes.
  */
-abstract class ReadOnlyStream implements StreamWrapperInterface {
-  /**
-   * Stream context resource.
-   *
-   * @var resource
-   */
-  public $context;
-
-  /**
-   * A generic resource handle.
-   *
-   * @var resource
-   */
-  public $handle = NULL;
-
-  /**
-   * Instance URI (stream).
-   *
-   * A stream is referenced as "scheme://target".
-   *
-   * @var string
-   */
-  protected $uri;
-
-  /**
-   * {@inheritdoc}
-   */
-  function setUri($uri) {
-    $this->uri = $uri;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  function getUri() {
-    return $this->uri;
-  }
+abstract class ReadOnlyStream extends StreamWrapperBase {
 
   /**
    * Support for fopen(), file_get_contents(), etc.
diff --git a/core/lib/Drupal/Core/StreamWrapper/StreamWrapperBase.php b/core/lib/Drupal/Core/StreamWrapper/StreamWrapperBase.php
new file mode 100644
index 0000000..b18ee05
--- /dev/null
+++ b/core/lib/Drupal/Core/StreamWrapper/StreamWrapperBase.php
@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StreamWrapper\StreamWrapperBase.
+ */
+
+namespace Drupal\Core\StreamWrapper;
+
+/**
+ * Provides a base class for all stream wrappers.
+ */
+abstract class StreamWrapperBase implements StreamWrapperInterface {
+
+  /**
+   * Stream context resource.
+   *
+   * @var resource
+   */
+  public $context;
+
+  /**
+   * A generic resource handle.
+   *
+   * @var resource
+   */
+  public $handle = NULL;
+
+  /**
+   * Instance URI (stream).
+   *
+   * A stream is referenced as "scheme://target".
+   *
+   * @var string
+   */
+  protected $uri;
+
+  /**
+   * {@inheritdoc}
+   */
+  function setUri($uri) {
+    if (strpos($uri, '://') === FALSE) {
+      // The delimiter ('://') was not found in $uri, malformed $uri passed.
+      throw new \InvalidArgumentException("Malformed uri parameter passed: {$this->uri}");
+    }
+    $this->uri = $uri;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  function getUri() {
+    return $this->uri;
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Theme/ThemeTest.php b/core/modules/system/src/Tests/Theme/ThemeTest.php
index 3d8b784..497c657 100644
--- a/core/modules/system/src/Tests/Theme/ThemeTest.php
+++ b/core/modules/system/src/Tests/Theme/ThemeTest.php
@@ -265,7 +265,7 @@ function testClassLoading() {
    */
   public function testFindThemeTemplates() {
     $registry = $this->container->get('theme.registry')->get();
-    $templates = drupal_find_theme_templates($registry, '.html.twig', drupal_get_path('theme', 'test_theme'));
+    $templates = drupal_find_theme_templates($registry, '.html.twig', 'theme://test_theme');
     $this->assertEqual($templates['node__1']['template'], 'node--1', 'Template node--1.tpl.twig was found in test_theme.');
   }
 
diff --git a/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php b/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php
index 565c6ef..f31d581 100644
--- a/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php
+++ b/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php
@@ -109,7 +109,7 @@ public function providerInvalidUris() {
    * Test the extension stream wrapper methods.
    *
    * @param string $uri
-   *   The uri to be tested,
+   *   The uri to be tested.
    * @param string|\InvalidArgumentException $dirname
    *   The expectation for dirname() method.
    * @param string|\InvalidArgumentException $realpath