Resize and save custom wallpaper to large and small size

ash/desktop_background/desktop_background_controller.h

Index: ash/desktop_background/desktop_background_controller.h
diff --git a/ash/desktop_background/desktop_background_controller.h b/ash/desktop_background/desktop_background_controller.h
index 3d2c919d41e95bbbc943ff29d933c80b05a262ae..0251c1c8d4e84af333c2458976a2847cf56f85b9 100644
--- a/ash/desktop_background/desktop_background_controller.h
+++ b/ash/desktop_background/desktop_background_controller.h
@@ -24,6 +24,15 @@ class RootWindow;
 
 namespace ash {
 
+// The width and height of small/large resolution wallpaper. When screen size is
+// smaller than |kSmallWallpaperMaxWidth| and |kSmallWallpaperMaxHeight|, the
+// small resolution wallpaper should be used. Otherwise, uses the large
+// resolution wallpaper.
+ASH_EXPORT extern const int kSmallWallpaperMaxWidth;
+ASH_EXPORT extern const int kSmallWallpaperMaxHeight;
+ASH_EXPORT extern const int kLargeWallpaperMaxWidth;
+ASH_EXPORT extern const int kLargeWallpaperMaxHeight;
+
 class UserWallpaperDelegate {
  public:
   virtual ~UserWallpaperDelegate() {}