Avoid sending notifications when the bitmap data in history has not changed

chrome/browser/history/history_backend.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H_
 
 #include <set>
 #include <string>
 #include <utility>
@@ skipping 686 matching lines @@
       const IconURLSizesMap& icon_url_sizes) const;
 
   // Sets the sizes that the thumbnail database knows that the favicon at
   // |icon_id| is available from the web. See history_types.h for a more
   // detailed description of FaviconSizes.
   // Deletes any favicon bitmaps currently mapped to |icon_id| whose pixel
   // sizes are not contained in |favicon_sizes|.
   void SetFaviconSizes(FaviconID icon_id,
                        const FaviconSizes& favicon_sizes);
 
+  // Returns true if the bitmap data at |bitmap_id| equals |new_bitmap_data|.
+  bool IsFaviconBitmapDataEqual(
+      FaviconBitmapID bitmap_id,
+      const scoped_refptr<base::RefCountedMemory>& new_bitmap_data);
+
   // Returns true if there are favicons for |page_url| and one of the types in
   // |icon_types|.
   // |favicon_bitmap_results| is set to the favicon bitmaps which most closely
   // match |desired_size_in_dip| and |desired_scale_factors|. If
   // |desired_size_in_dip| is 0, the largest favicon bitmap with one of the icon
   // types in |icon_types| is returned. If |icon_types| contains multiple icon
   // types and there are several matched icon types in the database, results
   // will only be returned for a single icon type in the priority of
   // TOUCH_PRECOMPOSED_ICON, TOUCH_ICON, and FAVICON. See the comment for
   // GetFaviconResultsForBestMatch() for more details on how
@@ skipping 185 matching lines @@
   // Used to provide the Android ContentProvider APIs.
   scoped_ptr<AndroidProviderBackend> android_provider_backend_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H_