Extract colors from wallpaper and dynamically update login screen overlay

components/wallpaper/wallpaper_manager_base.h

 // Copyright 2014 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_WALLPAPER_WALLPAPER_MANAGER_BASE_H_
 #define COMPONENTS_WALLPAPER_WALLPAPER_MANAGER_BASE_H_
 
 #include <stddef.h>
 
 #include <deque>
@@ skipping 177 matching lines @@
    private:
     WallpaperManagerBase* wallpaper_manager_;  // not owned
 
     DISALLOW_COPY_AND_ASSIGN(TestApi);
   };
 
   class Observer {
    public:
     virtual ~Observer() {}
     virtual void OnWallpaperAnimationFinished(const AccountId& account_id) = 0;
+    virtual void OnColorCalculationComplete() {}

[xiyuan, 2017/06/13 23:23:48]

Document this and other methods in this interface. OnColorCalculationComplete by
the name itself is not clear when it is invoked, e.g. it is not obvious that
this would be called as a result of SetWallpaper call.

[Wenzhao (Colin) Zang, 2017/06/14 00:44:50]

I've tried my best to add comments to the other three methods, please modify if
needed. Thanks.

     virtual void OnUpdateWallpaperForTesting() {}
     virtual void OnPendingListEmptyForTesting() {}
   };
 
   // set path IDs for used directories
   static void SetPathIds(int dir_user_data_enum,
                          int dir_chromeos_wallpapers_enum,
                          int dir_chromeos_custom_wallpapers_enum);
 
   // Returns custom wallpaper directory by appending corresponding |sub_dir|.
@@ skipping 424 matching lines @@
 
   base::WeakPtrFactory<WallpaperManagerBase> weak_factory_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(WallpaperManagerBase);
 };
 
 }  // namespace wallpaper
 
 #endif  // COMPONENTS_WALLPAPER_WALLPAPER_MANAGER_BASE_H_