Refactor HistoryService to not send NOTIFICATION_FAVICON_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 d462b2ecee302da0f863265a16192aa4d1f5bf62..b17b35e74575f720dd2752b268f6cbd3fa43ab8f 100644
--- a/chrome/browser/history/history_backend.h
+++ b/chrome/browser/history/history_backend.h
@@ -119,6 +119,10 @@ class HistoryBackend : public base::RefCountedThreadSafe<HistoryBackend>,
     virtual void SetInMemoryBackend(
         scoped_ptr<InMemoryHistoryBackend> backend) = 0;
 
+    // Notify HistoryService that some URLs favicon changed that will forward
+    // the events to the FaviconChangedObservers in the correct thread.
+    virtual void NotifyFaviconChanged(const std::set<GURL>& urls) = 0;
+
     // Broadcasts the specified notification to the notification service.
     // This is implemented here because notifications must only be sent from
     // the main thread. This is the only method that doesn't identify the