Add baked-in favicons for default popular sites on NTP

components/ntp_tiles/icon_cacher.h

Index: components/ntp_tiles/icon_cacher.h
diff --git a/components/ntp_tiles/icon_cacher.h b/components/ntp_tiles/icon_cacher.h
index 22beeb6f48c415b3616e15c8c1a94a6b4b9b3c23..c5e4280da6476698a90f5261b068d4a2c38e0c20 100644
--- a/components/ntp_tiles/icon_cacher.h
+++ b/components/ntp_tiles/icon_cacher.h
@@ -24,6 +24,12 @@ class IconCacher {
   // newly fetched (false if it was already cached or could not be fetched).
   virtual void StartFetch(PopularSites::Site site,
                           const base::Callback<void(bool)>& done) = 0;
+
+  // Associates a sites with the given image resource. The resource is used as a
+  // default which means it falls back to it if there is no current image and
+  // will try to update it when requested.
+  virtual void AddDefaultImage(const PopularSites::Site& site,
+                               int image_resource_id) = 0;
 };
 
 }  // namespace ntp_tiles