Move all wallpaper file loading and decoding from DesktopBackgroundController to WallpaperManager.

ash/desktop_background/desktop_background_controller_test_api.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 ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_TEST_API_H_
+#define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_TEST_API_H_
+
+#include "ash/desktop_background/desktop_background_controller.h"
+
+namespace ash {
+
+class DesktopBackgroundController::TestAPI {
+ public:
+  explicit TestAPI(DesktopBackgroundController* controller);
+
+  void set_wallpaper_reload_delay_for_test(bool value);
+
+ private:
+  DesktopBackgroundController* controller_;
+};
+
+}  // namespace ash
+
+#endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_TEST_API_H_