Support undoing offline page deletion

chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageBridge.java

 // Copyright 2015 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.offlinepages;
 
 import org.chromium.base.ObserverList;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.base.annotations.CalledByNative;
@@ skipping 46 matching lines @@
          *
          * @param deletePageResult Result of deleting the page. Uses
          *     {@see org.chromium.components.offlinepages.DeletePageResult} enum.
          * @see OfflinePageBridge#deletePage()
          */
         @CalledByNative("DeletePageCallback")
         void onDeletePageDone(int deletePageResult);
     }
 
     /**
-     * Interface that provides listeners to be notified of changes to the offline page model.
+     * Base empty implementation observer class that provides listeners to be notified of changes to
+     * the offline page model.
      */
-    public interface OfflinePageModelObserver {
+    public abstract static class OfflinePageModelObserver {
         /**
          * Called when the native side of offline pages is loaded and now in usable state.
          */
-        void offlinePageModelLoaded();
+        public void offlinePageModelLoaded() {}
+
+        /**
+         * Called when the native side of offline pages is changed due to adding, removing or
+         * update an offline page.
+         */
+        public void offlinePageModelChanged() {}
     }
 
     private static int getFreeSpacePercentage() {
         return (int) (1.0 * OfflinePageUtils.getFreeSpaceInBytes()
                 / OfflinePageUtils.getTotalSpaceInBytes() * 100);
     }
 
     private static int getFreeSpaceMB() {
         return (int) (OfflinePageUtils.getFreeSpaceInBytes() / (1024 * 1024));
     }
@@ skipping 153 matching lines @@
 
     @CalledByNative
     private void offlinePageModelLoaded() {
         mIsNativeOfflinePageModelLoaded = true;
         for (OfflinePageModelObserver observer : mObservers) {
             observer.offlinePageModelLoaded();
         }
     }
 
     @CalledByNative
+    private void offlinePageModelChanged() {
+        for (OfflinePageModelObserver observer : mObservers) {
+            observer.offlinePageModelChanged();
+        }
+    }
+
+    @CalledByNative
     private static void createOfflinePageAndAddToList(List<OfflinePageItem> offlinePagesList,
             String url, long bookmarkId, String offlineUrl, long fileSize, int accessCount) {
         offlinePagesList.add(createOfflinePageItem(url, bookmarkId, offlineUrl, fileSize,
                 accessCount));
     }
 
     @CalledByNative
     private static OfflinePageItem createOfflinePageItem(
             String url, long bookmarkId, String offlineUrl, long fileSize, int accessCount) {
         return new OfflinePageItem(url, bookmarkId, offlineUrl, fileSize, accessCount);
@@ skipping 10 matching lines @@
     private native void nativeSavePage(long nativeOfflinePageBridge, SavePageCallback callback,
             WebContents webContents, long bookmarkId);
     private native void nativeMarkPageAccessed(long nativeOfflinePageBridge, long bookmarkId);
     private native void nativeDeletePage(long nativeOfflinePageBridge,
             DeletePageCallback callback, long bookmarkId);
     private native void nativeDeletePages(
             long nativeOfflinePageBridge, DeletePageCallback callback, long[] bookmarkIds);
     private native void nativeGetPagesToCleanUp(
             long nativeOfflinePageBridge, List<OfflinePageItem> offlinePages);
 }