Reland - cros: Add CHECK for screen unlock problem

ash/desktop_background/desktop_background_widget_controller.h

 // Copyright (c) 2012 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_WIDGET_CONTROLLER_H_
 #define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_WIDGET_CONTROLLER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "ui/aura/window_property.h"
 #include "ui/compositor/layer.h"
@@ skipping 19 matching lines @@
   virtual ~DesktopBackgroundWidgetController();
 
   // Overridden from views::WidgetObserver.
   virtual void OnWidgetClosing(views::Widget* widget) OVERRIDE;
 
   // Set bounds of component that draws background.
   void SetBounds(gfx::Rect bounds);
 
   // Move component from |src_container| in |root_window| to |dest_container|.
   // It is required for lock screen, when we need to move background so that
-  // it hides user's windows.
-  void Reparent(aura::RootWindow* root_window,
+  // it hides user's windows. Returns true if there was something to reparent.
+  bool Reparent(aura::RootWindow* root_window,
                 int src_container,
                 int dest_container);
 
   views::Widget* widget() { return widget_; }
   ui::Layer* layer() { return layer_.get(); }
 
  private:
   views::Widget* widget_;
   scoped_ptr<ui::Layer> layer_;
 
@@ skipping 25 matching lines @@
 // to root windows.
 extern const aura::WindowProperty<DesktopBackgroundWidgetController*>* const
     kWindowDesktopComponent;
 
 extern const aura::WindowProperty<ComponentWrapper*>* const kComponentWrapper;
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_WIDGET_CONTROLLER_H_