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..d3aff0651c523ecddd93ce0b334d558014cb607b 100644
--- a/components/ntp_tiles/icon_cacher.h
+++ b/components/ntp_tiles/icon_cacher.h
@@ -21,9 +21,12 @@ class IconCacher {
   virtual ~IconCacher() = default;
 
   // Fetches the icon if necessary, then invokes |done| with true if it was
-  // newly fetched (false if it was already cached or could not be fetched).
+  // newly fetched or a default icon was loaded for the first time.
+  // It's invoked with False if it was already cached or could not be fetched.
+  // The callback will be invoked twice if a default icon was returned in the
+  // first place.
   virtual void StartFetch(PopularSites::Site site,
-                          const base::Callback<void(bool)>& done) = 0;
+                          const base::Callback<void(bool)>& icon_available) = 0;
 };
 
 }  // namespace ntp_tiles