[Icon cacher] Add metrics for downloading favicons for NTP Tiles

components/ntp_tiles/icon_cacher_impl.h

Index: components/ntp_tiles/icon_cacher_impl.h
diff --git a/components/ntp_tiles/icon_cacher_impl.h b/components/ntp_tiles/icon_cacher_impl.h
index 85d02b760f1e7ac6752aeecdfe85dfa62d3b5e07..a124b2c21d2c0a72ab1ebd77388cbf0a2c20c77d 100644
--- a/components/ntp_tiles/icon_cacher_impl.h
+++ b/components/ntp_tiles/icon_cacher_impl.h
@@ -83,6 +83,8 @@ class IconCacherImpl : public IconCacher {
       const GURL& page_url,
       const favicon_base::LargeIconResult& result);
 
+  void OnMostLikelyFaviconDownloaded(const GURL& request_url, bool success);
+
   bool StartRequest(const GURL& request_url,
                     const base::Closure& icon_available);
   void FinishRequestAndNotifyIconAvailable(const GURL& request_url,