reverted:
--- b/core/modules/image/src/Entity/ImageStyle.php
+++ a/core/modules/image/src/Entity/ImageStyle.php
@@ -307,15 +307,6 @@
   /**
    * {@inheritdoc}
    */
-  public function transformMimeType(&$mime_type) {
-    foreach ($this->getEffects() as $effect) {
-      $effect->transformMimeType($mime_type);
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function getPathToken($uri) {
     // Return the first 8 characters.
     return substr(Crypt::hmacBase64($this->id() . ':' . $uri, \Drupal::service('private_key')->get() . Settings::getHashSalt()), 0, 8);
@@ -342,7 +333,7 @@
    */
   public function getEffects() {
     if (!$this->effectsBag) {
+      $this->effectsBag = new ImageEffectBag(\Drupal::service('plugin.manager.image.effect'), $this->effects);
-      $this->effectsBag = new ImageEffectBag($this->getImageEffectPluginManager(), $this->effects);
       $this->effectsBag->sort();
     }
     return $this->effectsBag;
@@ -386,11 +377,4 @@
     return $this;
   }
  
-  /**
-   * {@inheritdoc}
-   */
-  public function getImageEffectPluginManager() {
-    return \Drupal::service('plugin.manager.image.effect');
-  }
-
 }
reverted:
--- b/core/modules/image/src/ImageEffectBase.php
+++ a/core/modules/image/src/ImageEffectBase.php
@@ -77,12 +77,6 @@
   /**
    * {@inheritdoc}
    */
-  public function transformMimeType(&$mime_type) {
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function getSummary() {
     return array(
       '#markup' => '',
reverted:
--- b/core/modules/image/src/ImageEffectInterface.php
+++ a/core/modules/image/src/ImageEffectInterface.php
@@ -44,14 +44,6 @@
   public function transformDimensions(array &$dimensions);
  
   /**
-   * Determines the MIME type of the image effect.
-   *
-   * @param string $mime_type
-   *   The MIME type to be modified.
-   */
-  public function transformMimeType(&$mime_type);
-
-  /**
    * Returns a render array summarizing the configuration of the image effect.
    *
    * @return array
reverted:
--- b/core/modules/image/src/ImageStyleInterface.php
+++ a/core/modules/image/src/ImageStyleInterface.php
@@ -131,14 +131,6 @@
   public function transformDimensions(array &$dimensions);
  
   /**
-   * Determines the MIME type of the image style.
-   *
-   * @param string $mime_type
-   *   The MIME type to be modified.
-   */
-  public function transformMimeType(&$mime_type);
-
-  /**
    * Returns a specific image effect.
    *
    * @param string $effect
@@ -178,12 +170,4 @@
    */
   public function deleteImageEffect(ImageEffectInterface $effect);
  
-  /**
-   * Returns the image effect plugin manager.
-   *
-   * @return \Drupal\Component\Plugin\PluginManagerInterface
-   *   The image effect plugin manager.
-   */
-  public function getImageEffectPluginManager();
-
 }
reverted:
--- b/core/modules/image/src/Tests/ImageStyleTest.php
+++ /dev/null
@@ -1,111 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\image\Tests\ImageStyleTest.
- */
-
-namespace Drupal\image\Tests;
-
-use Drupal\Tests\UnitTestCase;
-
-/**
- * @coversDefaultClass \Drupal\image\Entity\ImageStyle
- *
- * @group Drupal
- * @group Image
- */
-class ImageStyleTest extends UnitTestCase {
-
-  /**
-   * The entity type used for testing.
-   *
-   * @var \Drupal\Core\Entity\EntityTypeInterface|\PHPUnit_Framework_MockObject_MockObject
-   */
-  protected $entityType;
-
-  /**
-   * The entity manager used for testing.
-   *
-   * @var \Drupal\Core\Entity\EntityManagerInterface|\PHPUnit_Framework_MockObject_MockObject
-   */
-  protected $entityManager;
-
-  /**
-   * The ID of the type of the entity under test.
-   *
-   * @var string
-   */
-  protected $entityTypeId;
-
-  /**
-   * The effect manager used for testing.
-   *
-   * @var \Drupal\image\ImageEffectManager|\PHPUnit_Framework_MockObject_MockObject
-   */
-  protected $effectManager;
-
-  /**
-   * The image effect used for testing.
-   *
-   * @var \Drupal\image\ImageEffectInterface|\PHPUnit_Framework_MockObject_MockObject
-   */
-  protected $imageEffect;
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setUp() {
-    $this->entityTypeId = $this->randomMachineName();
-    $this->provider = $this->randomMachineName();
-    $this->entityType = $this->getMock('\Drupal\Core\Entity\EntityTypeInterface');
-    $this->entityType->expects($this->any())
-      ->method('getProvider')
-      ->will($this->returnValue($this->provider));
-    $this->entityManager = $this->getMock('\Drupal\Core\Entity\EntityManagerInterface');
-    $this->entityManager->expects($this->any())
-      ->method('getDefinition')
-      ->with($this->entityTypeId)
-      ->will($this->returnValue($this->entityType));
-    $this->effectManager = $this->getMockBuilder('\Drupal\image\ImageEffectManager')
-      ->disableOriginalConstructor()
-      ->getMock();
-  }
-
-  /**
-   * @covers ::transformMimeType
-   */
-  public function testTransformMimeType() {
-    $image_effect_id = $this->randomMachineName();
-    $logger = $this->getMockBuilder('\Psr\Log\LoggerInterface')->getMock();
-    $image_effect = $this->getMockBuilder('\Drupal\image\ImageEffectBase')
-      ->setConstructorArgs(array(array(), $image_effect_id, array(), $logger))
-      ->getMock();
-    $image_effect->expects($this->any())
-      ->method('transformMimeType')
-      ->will($this->returnCallback(function (&$mime_type) { $mime_type = 'image/webp';}));
-
-    $this->effectManager->expects($this->any())
-      ->method('createInstance')
-      ->with($image_effect_id)
-      ->will($this->returnValue($image_effect));
-
-    $image_style = $this->getMockBuilder('\Drupal\image\Entity\ImageStyle')
-      ->setConstructorArgs(array(
-        array('effects' => array($image_effect_id => array('id' => $image_effect_id))),
-        $this->entityTypeId,
-      ))
-      ->setMethods(array('getImageEffectPluginManager'))
-      ->getMock();
-    $image_style->expects($this->any())
-      ->method('getImageEffectPluginManager')
-      ->will($this->returnValue($this->effectManager));
-
-    $mime_types = array('image/jpeg', 'image/gif', 'image/png');
-    foreach ($mime_types as $mime_type) {
-      $image_style->transformMimeType($mime_type);
-      $this->assertEquals($mime_type, 'image/webp');
-    }
-  }
-
-}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/src/Tests/Theme/ImageTest.php
@@ -0,0 +1,98 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\system\Tests\Theme\ImageTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\DrupalUnitTestBase;
+
+/**
+ * Tests built-in image theme functions.
+ *
+ * @group Theme
+ */
+class ImageTest extends DrupalUnitTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('system');
+
+  /**
+   * The images to test with.
+   *
+   * @var array
+   */
+  protected $testImages;
+
+  protected function setUp() {
+    parent::setUp();
+    $this->testImages = array(
+      DRUPAL_ROOT . '/core/misc/druplicon.png',
+      DRUPAL_ROOT . '/core/misc/loading.gif',
+      DRUPAL_ROOT . '/core/misc/loading-small.gif',
+    );
+  }
+
+  /**
+   * Tests that an image with the src attribute is outputted correctly.
+   */
+  function testThemeImageWithSrc() {
+
+    $image = array(
+      '#theme' => 'image',
+      '#uri' => reset($this->testImages),
+      '#width' => rand(0, 1000) . 'px',
+      '#height' => rand(0, 500) . 'px',
+      '#alt' => $this->randomString(),
+      '#title' => $this->randomString(),
+    );
+    $this->render($image);
+    $this->removeWhiteSpace();
+    $expected = '<img src="' . $image['#uri'] . '" width="' . $image['#width']
+      . '" height="' . $image['#height'] . '" alt="' . $image['#alt']
+      . '" title="' . $image['#title'] . '" />';
+    $this->assertRaw($expected, 'Correct output for image with src attribute.');
+  }
+
+  /**
+   * Tests that an image with the srcset attribute is outputted correctly.
+   */
+  function testThemeImageWithSrcset() {
+    // Test with multipliers.
+    $image = array(
+      '#theme' => 'image',
+      '#srcset' => array(
+        array(
+          'uri' => $this->testImages[0],
+          'multiplier' => '1x',
+        ),
+        array(
+          'uri' => $this->testImages[1],
+          'multiplier' => '2x',
+        ),
+        array(
+          'uri' => $this->testImages[2],
+          'width' => '640w',
+        ),
+      ),
+      '#width' => rand(0, 1000) . 'px',
+      '#height' => rand(0, 500) . 'px',
+      '#alt' => $this->randomString(),
+      '#title' => $this->randomString(),
+    );
+    $this->render($image);
+    $this->removeWhiteSpace();
+    $expected = '<img srcset="' . $this->testImages[0] . ' 1x, '
+      . $this->testImages[1] . ' 2x, ' . $this->testImages[2] . ' 640w" width="'
+      . $image['#width'] . '" height="' . $image['#height'] . '" alt="'
+      . $image['#alt'] . '" title="' . $image['#title'] . '" />';
+    $this->assertRaw($expected, 'Correct output for image with srcset attribute.');
+  }
+
+}