Fix white flash when user sings out and wallpaper animation regression

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"
 #include "ui/views/widget/widget.h"
 
 namespace ash {
 namespace internal {
 
 // This class hides difference between two possible background implementations:
 // effective Layer-based for solid color, and Widget-based for images.
+// DesktopBackgroundWidgetController is installed as an owned property on the
+// RootWindow. To avoid a white flash during wallpaper changes the old
+// DesktopBackgroundWidgetController is moved to a secondary property
+// (kComponentWrapper). When the animation completes the old
+// DesktopBackgroundWidgetController is destroyed.
 class DesktopBackgroundWidgetController {
  public:
   // Create
   explicit DesktopBackgroundWidgetController(views::Widget* widget);
   explicit DesktopBackgroundWidgetController(ui::Layer* layer);
 
   ~DesktopBackgroundWidgetController();
 
   // 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,
                 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_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundWidgetController);
 };
 
+// This class wraps a DesktopBackgroundWidgetController pointer. It is installed
+// as an owned property on the RootWindow. DesktopBackgroundWidgetController is
+// moved to this property before animation completes. After animation completes,
+// the kWindowDesktopComponent property on RootWindow is set to the
+// DesktopBackgroundWidgetController in this class.
+class ComponentWrapper {
+ public:
+  explicit ComponentWrapper(
+      DesktopBackgroundWidgetController* component);
+  ~ComponentWrapper() {}
+  DesktopBackgroundWidgetController* component() { return component_; }
+
+ private:
+  DesktopBackgroundWidgetController* component_;
+
+  DISALLOW_COPY_AND_ASSIGN(ComponentWrapper);
+};
+
 // Window property key, that binds instance of DesktopBackgroundWidgetController
 // 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_