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..e7456fd0a9cc9792fe856d720df2f55f6e683725 100644
--- a/components/ntp_tiles/icon_cacher.h
+++ b/components/ntp_tiles/icon_cacher.h
@@ -20,10 +20,14 @@ class IconCacher {
  public:
   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).
+  // Fetches the icon if necessary. It invokes |icon_available| if a new icon
+  // was fetched. This is the only required callback.
+  // If there are preliminary icons (e.g. provided by static resources), the
+  // |preliminary_icon_available| callback will be invoked additionally.
+  // TODO(fhorschig): In case we keep these, make them OnceClosures.
   virtual void StartFetch(PopularSites::Site site,
-                          const base::Callback<void(bool)>& done) = 0;
+                          const base::Closure& icon_available,
+                          const base::Closure& preliminary_icon_available) = 0;
 };
 
 }  // namespace ntp_tiles