Extract colors from wallpaper and dynamically update login screen overlay

components/wallpaper/wallpaper_manager_base.h

Index: components/wallpaper/wallpaper_manager_base.h
diff --git a/components/wallpaper/wallpaper_manager_base.h b/components/wallpaper/wallpaper_manager_base.h
index 88601cc801e5ad5ce87d5e76e460f08e75e5e7b9..62a995e2f6b1692ef45c7c2edb57702584a9fa27 100644
--- a/components/wallpaper/wallpaper_manager_base.h
+++ b/components/wallpaper/wallpaper_manager_base.h
@@ -195,6 +195,7 @@ class WALLPAPER_EXPORT WallpaperManagerBase {
    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() {}
   };