diff --git a/core/core.services.yml b/core/core.services.yml
index 55384a7..dc79944 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1515,10 +1515,8 @@ services:
     arguments: ['@render_strategy_manager']
   render_strategy_manager:
     class: Drupal\Core\Render\Strategy\RenderStrategyManager
-    arguments: ['@renderer']
     tags:
       - { name: service_collector, tag: render_strategy, call: addRenderStrategy }
-    lazy: true
   render_strategy.single_flush:
     class: Drupal\Core\Render\Strategy\SingleFlushRenderStrategy
     tags:
diff --git a/core/lib/Drupal/Core/EventSubscriber/HtmlRenderStrategySubscriber.php b/core/lib/Drupal/Core/EventSubscriber/HtmlRenderStrategySubscriber.php
index d40f451..c93e0b0 100644
--- a/core/lib/Drupal/Core/EventSubscriber/HtmlRenderStrategySubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/HtmlRenderStrategySubscriber.php
@@ -8,35 +8,35 @@
 namespace Drupal\Core\EventSubscriber;
 
 use Drupal\Core\Render\HtmlResponse;
-use Drupal\Core\Render\Strategy\RenderStrategyManagerInterface;
+use Drupal\Core\Render\Strategy\RenderStrategyInterface;
 use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
 use Symfony\Component\HttpKernel\KernelEvents;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 
 /**
- * Response subscriber to handle render strategies for HTML responses.
+ * HTML Response subscriber to handle placeholder render strategies.
  */
 class HtmlRenderStrategySubscriber implements EventSubscriberInterface {
 
   /**
    * The render strategy manager service.
    *
-   * @var \Drupal\Core\Render\Strategy\RenderStrategyManager
+   * @var \Drupal\Core\Render\Strategy\RenderStrategyInterface
    */
   protected $renderStrategyManager;
 
   /**
    * Constructs a HtmlRenderStrategySubscriber object.
    *
-   * @param \Drupal\Core\Render\Strategy\RenderStrategyManagerInterface $render_strategy_manager
+   * @param \Drupal\Core\Render\Strategy\RenderStrategyInterface $render_strategy_manager
    *   The render strategy manager service.
    */
-  public function __construct(RenderStrategyManagerInterface $render_strategy_manager) {
+  public function __construct(RenderStrategyInterface $render_strategy_manager) {
     $this->renderStrategyManager = $render_strategy_manager;
   }
 
   /**
-   * Processes attachments for HtmlResponse responses.
+   * Processes placeholders for HtmlResponse responses.
    *
    * @param \Symfony\Component\HttpKernel\Event\FilterResponseEvent $event
    *   The event to process.
diff --git a/core/lib/Drupal/Core/ProxyClass/Render/Strategy/RenderStrategyManager.php b/core/lib/Drupal/Core/ProxyClass/Render/Strategy/RenderStrategyManager.php
deleted file mode 100644
index 7200c4d..0000000
--- a/core/lib/Drupal/Core/ProxyClass/Render/Strategy/RenderStrategyManager.php
+++ /dev/null
@@ -1,92 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\ProxyClass\Render\Strategy\RenderStrategyManager.
- */
-
-/**
- * This file was generated via php core/scripts/generate-proxy-class.php 'Drupal\Core\Render\Strategy\RenderStrategyManager' "core/lib/Drupal/Core".
- */
-
-namespace Drupal\Core\ProxyClass\Render\Strategy {
-
-    /**
-     * Provides a proxy class for \Drupal\Core\Render\Strategy\RenderStrategyManager.
-     *
-     * @see \Drupal\Component\ProxyBuilder
-     */
-    class RenderStrategyManager implements \Drupal\Core\Render\Strategy\RenderStrategyManagerInterface
-    {
-
-        use \Drupal\Core\DependencyInjection\DependencySerializationTrait;
-
-        /**
-         * The id of the original proxied service.
-         *
-         * @var string
-         */
-        protected $drupalProxyOriginalServiceId;
-
-        /**
-         * The real proxied service, after it was lazy loaded.
-         *
-         * @var \Drupal\Core\Render\Strategy\RenderStrategyManager
-         */
-        protected $service;
-
-        /**
-         * The service container.
-         *
-         * @var \Symfony\Component\DependencyInjection\ContainerInterface
-         */
-        protected $container;
-
-        /**
-         * Constructs a ProxyClass Drupal proxy object.
-         *
-         * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
-         *   The container.
-         * @param string $drupal_proxy_original_service_id
-         *   The service ID of the original service.
-         */
-        public function __construct(\Symfony\Component\DependencyInjection\ContainerInterface $container, $drupal_proxy_original_service_id)
-        {
-            $this->container = $container;
-            $this->drupalProxyOriginalServiceId = $drupal_proxy_original_service_id;
-        }
-
-        /**
-         * Lazy loads the real service from the container.
-         *
-         * @return object
-         *   Returns the constructed real service.
-         */
-        protected function lazyLoadItself()
-        {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
-
-            return $this->service;
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function addRenderStrategy(\Drupal\Core\Render\Strategy\RenderStrategyInterface $strategy)
-        {
-            return $this->lazyLoadItself()->addRenderStrategy($strategy);
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function processPlaceholders(array $placeholders)
-        {
-            return $this->lazyLoadItself()->processPlaceholders($placeholders);
-        }
-
-    }
-
-}
diff --git a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
index 728599a..cc20063 100644
--- a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
+++ b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
@@ -182,31 +182,6 @@ protected function renderPlaceholders(HtmlResponse $response) {
     return $response;
   }
 
- /**
-   * Renders placeholders (#attached[placeholders]).
-   *
-   * @param \Drupal\Core\Render\HtmlResponse $response
-   *   The HTML response whose placeholders to replace.
-   *
-   * @see \Drupal\Core\Render\Renderer::replacePlaceholders()
-   * @see \Drupal\Core\Render\Renderer::renderPlaceholder()
-   */
-  protected function renderPlaceholders(HtmlResponse $response) {
-    // Render the placeholders in the HTML Response object.
-    $build = [
-      '#markup' => SafeString::create($response->getContent()),
-      '#attached' => $response->getAttachments(),
-    ];
-    $this->renderer->renderRoot($build);
-
-    // Update the Response object now that the placeholders have been rendered.
-    $placeholders_bubbleable_metadata = BubbleableMetadata::createFromRenderArray($build);
-    $response
-      ->setContent($build['#markup'])
-      ->addCacheableDependency($placeholders_bubbleable_metadata)
-      ->setAttachments($placeholders_bubbleable_metadata->getAttachments());
-  }
-
   /**
    * Processes asset libraries into render arrays.
    *
diff --git a/core/lib/Drupal/Core/Render/Renderer.php b/core/lib/Drupal/Core/Render/Renderer.php
index 681af5b..e9a9634 100644
--- a/core/lib/Drupal/Core/Render/Renderer.php
+++ b/core/lib/Drupal/Core/Render/Renderer.php
@@ -258,8 +258,6 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
     // - this is a render cacheable subtree, to ensure that the cached data has
     //   the configurable defaults (which may affect the ID and invalidation).
     if ($is_root_call || isset($elements['#cache']['keys'])) {
-      // This is inlined for performance reasons. Also see
-      // applyRequiredCacheContexts() function below.
       $required_cache_contexts = $this->rendererConfig['required_cache_contexts'];
       if (isset($elements['#cache']['contexts'])) {
         $elements['#cache']['contexts'] = Cache::mergeContexts($elements['#cache']['contexts'], $required_cache_contexts);
@@ -564,21 +562,6 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
   /**
    * {@inheritdoc}
    */
-  public function applyRequiredCacheContexts(array $elements) {
-    $required_cache_contexts = $this->rendererConfig['required_cache_contexts'];
-    if (isset($elements['#cache']['contexts'])) {
-      $elements['#cache']['contexts'] = Cache::mergeContexts($elements['#cache']['contexts'], $required_cache_contexts);
-    }
-    else {
-      $elements['#cache']['contexts'] = $required_cache_contexts;
-    }
-
-    return $elements;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function hasRenderContext() {
     return (bool) $this->getCurrentRenderContext();
   }
diff --git a/core/lib/Drupal/Core/Render/RendererInterface.php b/core/lib/Drupal/Core/Render/RendererInterface.php
index c2c3012..155eec4 100644
--- a/core/lib/Drupal/Core/Render/RendererInterface.php
+++ b/core/lib/Drupal/Core/Render/RendererInterface.php
@@ -365,21 +365,6 @@ public function hasRenderContext();
   public function executeInRenderContext(RenderContext $context, callable $callable);
 
   /**
-   * Applies the required cache contexts to a render array.
-   *
-   * Note: This function should only be needed in edge-case circumstances; e.g.
-   * when interacting directly with the RenderCache class or by rendering
-   * without replacing placeholders.
-   *
-   * @param array $elements
-   *   The render array to apply the required cache contexts to.
-   *
-   * @return array
-   *   A render array with the required cache contexts added.
-   */
-  public function applyRequiredCacheContexts(array $elements);
-
-  /**
    * Merges the bubbleable rendering metadata o/t 2nd render array with the 1st.
    *
    * @param array $a
diff --git a/core/lib/Drupal/Core/Render/Strategy/RenderStrategyManager.php b/core/lib/Drupal/Core/Render/Strategy/RenderStrategyManager.php
index 2a18a72..9f188e0 100644
--- a/core/lib/Drupal/Core/Render/Strategy/RenderStrategyManager.php
+++ b/core/lib/Drupal/Core/Render/Strategy/RenderStrategyManager.php
@@ -12,14 +12,7 @@
 /**
  * Provides a class which allows to render placeholders.
  */
-class RenderStrategyManager implements RenderStrategyManagerInterface {
-
-  /**
-   * The renderer.
-   *
-   * @var \Drupal\Core\Render\RendererInterface
-   */
-  protected $renderer;
+class RenderStrategyManager implements RenderStrategyInterface {
 
   /**
    * The RenderStrategy services.
@@ -29,16 +22,6 @@ class RenderStrategyManager implements RenderStrategyManagerInterface {
   protected $renderStrategies;
 
   /**
-   * Constructs a new RenderStrategyManager class.
-   *
-   * @param \Drupal\Core\Render\RendererInterface
-   *   The renderer.
-   */
-  public function __construct(RendererInterface $renderer) {
-    $this->renderer = $renderer;
-  }
-
-  /**
    * Adds a render strategy to process.
    *
    * @param RenderStrategyInterface $strategy
diff --git a/core/lib/Drupal/Core/Render/Strategy/RenderStrategyManagerInterface.php b/core/lib/Drupal/Core/Render/Strategy/RenderStrategyManagerInterface.php
deleted file mode 100644
index 0120f50..0000000
--- a/core/lib/Drupal/Core/Render/Strategy/RenderStrategyManagerInterface.php
+++ /dev/null
@@ -1,26 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Render\Strategy\RenderStrategyManagerInterface.
- */
-
-namespace Drupal\Core\Render\Strategy;
-
-/**
- * Provides an interface which allows to process placeholders.
- */
-interface RenderStrategyManagerInterface {
-
-  /**
-   * Processes placeholders with different strategies.
-   *
-   * @param array $placeholders
-   *   The placeholders to process.
-   *
-   * @return array
-   *   The processed placeholders.
-   */
-  public function processPlaceholders(array $placeholders);
-
-}
diff --git a/core/tests/Drupal/Tests/Core/Render/Strategy/RenderStrategyManagerTest.php b/core/tests/Drupal/Tests/Core/Render/Strategy/RenderStrategyManagerTest.php
new file mode 100644
index 0000000..329159b
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Render/Strategy/RenderStrategyManagerTest.php
@@ -0,0 +1,123 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\Render\Strategy\RenderStrategyManagerTest.
+ */
+
+namespace Drupal\Tests\Core\Render\Strategy;
+
+use Drupal\Core\Render\Strategy\RenderStrategyManager;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Render\Strategy\RenderStrategyManager
+ * @group Render
+ */
+class RenderStrategyManagerTest extends UnitTestCase {
+
+  /**
+   * @covers ::addRenderStrategy
+   * @covers ::processPlaceholders
+   *
+   * @dataProvider providerProcessPlaceholders
+   */
+  public function testProcessPlaceholdersSingleFlush($strategies, $placeholders, $result) {
+    $render_strategy_manager = new RenderStrategyManager();
+
+    foreach ($strategies as $strategy) {
+      $render_strategy_manager->addRenderStrategy($strategy);
+    }
+
+    $this->assertEquals($result, $render_strategy_manager->processPlaceholders($placeholders));
+  }
+
+  /**
+   * Provides a list of render strategies, placeholders and results.
+   *
+   * @return array
+   */
+  public function providerProcessPlaceholders() {
+    $data = [];
+
+    // Empty placeholders.
+    $data[] = [[], [], []];
+
+    // Placeholder removing strategy.
+    $placeholders = [
+      'remove-me' => ['#markup' => 'I-am-a-llama-that-will-be-removed-sad-face.'],
+    ];
+
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Strategy\RenderStrategyInterface');
+    $prophecy->processPlaceholders($placeholders)->willReturn([]);
+    $dev_null_strategy = $prophecy->reveal();
+
+    $data[] = [[$dev_null_strategy], $placeholders, []];
+
+    // Fake Single Flush strategy.
+    $placeholders = [
+      '67890' => ['#markup' => 'special-placeholder'],
+    ];
+
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Strategy\RenderStrategyInterface');
+    $prophecy->processPlaceholders($placeholders)->willReturn($placeholders);
+    $single_flush_strategy = $prophecy->reveal();
+
+    $data[] = [[$single_flush_strategy], $placeholders, $placeholders];
+
+    // Fake ESI strategy.
+    $placeholders = [
+      '12345' => ['#markup' => 'special-placeholder-for-esi'],
+    ];
+    $result = [
+      '12345' => ['#markup' => '<esi:include src="/fragment/12345" />'],
+    ];
+
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Strategy\RenderStrategyInterface');
+    $prophecy->processPlaceholders($placeholders)->willReturn($result);
+    $esi_strategy = $prophecy->reveal();
+
+    $data[] = [[$esi_strategy], $placeholders, $result];
+
+    // ESI + SingleFlush strategy (ESI replaces all).
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Strategy\RenderStrategyInterface');
+    $prophecy->processPlaceholders($placeholders)->willReturn($result);
+    $esi_strategy = $prophecy->reveal();
+
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Strategy\RenderStrategyInterface');
+    $single_flush_strategy = $prophecy->reveal();
+
+    $data[] = [[$esi_strategy, $single_flush_strategy], $placeholders, $result];
+
+    // ESI + SingleFlush strategy (mixed).
+    $placeholders = [
+      '12345' => ['#markup' => 'special-placeholder-for-ESI'],
+      '67890' => ['#markup' => 'special-placeholder'],
+      'foo' => ['#markup' => 'bar'],
+    ];
+
+    $esi_result = [
+      '12345' => ['#markup' => '<esi:include src="/fragment/12345" />'],
+    ];
+
+    $normal_result = [
+      '67890' => ['#markup' => 'special-placeholder'],
+      'foo' => ['#markup' => 'bar'],
+    ];
+
+    $result = $esi_result + $normal_result;
+
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Strategy\RenderStrategyInterface');
+    $prophecy->processPlaceholders($placeholders)->willReturn($esi_result);
+    $esi_strategy = $prophecy->reveal();
+
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Strategy\RenderStrategyInterface');
+    $prophecy->processPlaceholders($normal_result)->willReturn($normal_result);
+    $single_flush_strategy = $prophecy->reveal();
+
+    $data[] = [[$esi_strategy, $single_flush_strategy], $placeholders, $result];
+
+    return $data;
+  }
+
+}