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

chrome/browser/history/history_backend.h

Index: chrome/browser/history/history_backend.h
diff --git a/chrome/browser/history/history_backend.h b/chrome/browser/history/history_backend.h
index 7d3c50777763035c358bdffbd9b0f099f9796b64..bab856c4170a9511e9e8bd3f75d580b0fedb54f9 100644
--- a/chrome/browser/history/history_backend.h
+++ b/chrome/browser/history/history_backend.h
@@ -704,6 +704,11 @@ class HistoryBackend : public base::RefCountedThreadSafe<HistoryBackend>,
   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