Reland - cros: Add CHECK for screen unlock problem

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 0251c1c8d4e84af333c2458976a2847cf56f85b9..8976a31ed9ea3f20ebf8ed90ac1f2d4d01208d2b 100644
--- a/ash/desktop_background/desktop_background_controller.h
+++ b/ash/desktop_background/desktop_background_controller.h
@@ -120,10 +120,12 @@ class ASH_EXPORT DesktopBackgroundController : public aura::WindowObserver {
   WallpaperResolution GetAppropriateResolution();
 
   // Move all desktop widgets to locked container.
-  void MoveDesktopToLockedContainer();
+  // Returns true if the desktop moved.
+  bool MoveDesktopToLockedContainer();
 
   // Move all desktop widgets to unlocked container.
-  void MoveDesktopToUnlockedContainer();
+  // Returns true if the desktop moved.
+  bool MoveDesktopToUnlockedContainer();
 
   // WindowObserver implementation.
   virtual void OnWindowDestroying(aura::Window* window) OVERRIDE;
@@ -155,9 +157,9 @@ class ASH_EXPORT DesktopBackgroundController : public aura::WindowObserver {
   // all root windows.
   void InstallComponentForAllWindows();
 
-  // Moves all descktop components from one container to other across all root
-  // windows.
-  void ReparentBackgroundWidgets(int src_container, int dst_container);
+  // Moves all desktop components from one container to other across all root
+  // windows. Returns true if a desktop moved.
+  bool ReparentBackgroundWidgets(int src_container, int dst_container);
 
   // Returns id for background container for unlocked and locked states.
   int GetBackgroundContainerId(bool locked);