[Suggestions UI] Drop Bitmap references from articles under memory pressure.

chrome/android/java/src/org/chromium/chrome/browser/suggestions/SuggestionsUiDelegate.java

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.suggestions;
 
+import org.chromium.base.DiscardableReferencePool;
 import org.chromium.chrome.browser.favicon.FaviconHelper.FaviconImageCallback;
 import org.chromium.chrome.browser.favicon.FaviconHelper.IconAvailabilityCallback;
 import org.chromium.chrome.browser.favicon.LargeIconBridge.LargeIconCallback;
 import org.chromium.chrome.browser.ntp.snippets.SuggestionsSource;
 
 /**
  * Interface between the suggestion surface and the rest of the browser.
  */
 public interface SuggestionsUiDelegate {
     // Dependency injection
     // TODO(dgn): remove these methods once the users have a different way to get a reference
     // to these objects (https://crbug.com/677672)
 
     /** Convenience method to access the {@link SuggestionsSource}. */
     SuggestionsSource getSuggestionsSource();
 
     /** Convenience method to access the {@link SuggestionsRanker}. */
     SuggestionsRanker getSuggestionsRanker();
 
     /** Convenience method to access the {@link SuggestionsEventReporter}. */
     SuggestionsEventReporter getEventReporter();
 
     /** Convenience method to access the {@link SuggestionsNavigationDelegate}. */
     SuggestionsNavigationDelegate getNavigationDelegate();
 
+    /**
+     * @return The reference pool to use for large objects that should be dropped under
+     * memory pressure.
+     */
+    DiscardableReferencePool getReferencePool();
+
     // Favicons
 
     /**
      * Checks if an icon with the given URL is available. If not,
      * downloads it and stores it as a favicon/large icon for the given {@code pageUrl}.
      * @param pageUrl The URL of the site whose icon is being requested.
      * @param iconUrl The URL of the favicon/large icon.
      * @param isLargeIcon Whether the {@code iconUrl} represents a large icon or favicon.
      * @param callback The callback to be notified when the favicon has been checked.
      */
@@ skipping 16 matching lines @@
      */
     void getLocalFaviconImageForURL(String url, int size, FaviconImageCallback faviconCallback);
 
     // Feature/State checks
 
     /**
      * Registers a {@link DestructionObserver}, notified when the New Tab Page goes away.
      */
     void addDestructionObserver(DestructionObserver destructionObserver);
 
-    /** @return whether the suggestions UI is currently visible. */
+    /** @return Whether the suggestions UI is currently visible. */
     boolean isVisible();
 }