Add baked-in favicons for default popular sites on NTP

components/ntp_tiles/icon_cacher_impl.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_NTP_TILES_ICON_CACHER_IMPL_H_
 #define COMPONENTS_NTP_TILES_ICON_CACHER_IMPL_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 21 matching lines @@
 
 namespace ntp_tiles {
 
 class IconCacherImpl : public IconCacher {
  public:
   IconCacherImpl(favicon::FaviconService* favicon_service,
                  std::unique_ptr<image_fetcher::ImageFetcher> image_fetcher);
   ~IconCacherImpl() override;
 
   void StartFetch(PopularSites::Site site,
                   const base::Callback<void(bool)>& done) override;

[sfiera, 2017/02/16 18:54:16]

If I see a callback "done" I assume it's going to be called once. Can you change
the name and add a comment explaining how many times it will be called and when?

[fhorschig, 2017/02/17 16:24:03]

I added a comment and changed the name. 
Strictly, I expect only OnceCallback to be called once.

 
  private:
   void OnGetFaviconImageForPageURLFinished(
       PopularSites::Site site,
       const base::Callback<void(bool)>& done,
       const favicon_base::FaviconImageResult& result);
 
   void OnFaviconDownloaded(PopularSites::Site site,
                            const base::Callback<void(bool)>& done,
                            const std::string& id,
                            const gfx::Image& fetched_image);
 
+  bool ProvideDefaultIcon(const PopularSites::Site& site);
+  void SaveIconForSite(const PopularSites::Site& site, const gfx::Image image);
+
   base::CancelableTaskTracker tracker_;
   favicon::FaviconService* const favicon_service_;
   std::unique_ptr<image_fetcher::ImageFetcher> const image_fetcher_;
 
   DISALLOW_COPY_AND_ASSIGN(IconCacherImpl);
 };
 
 }  // namespace ntp_tiles
 
 #endif  // COMPONENTS_NTP_TILES_ICON_CACHER_IMPL_H_