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.
 class DesktopBackgroundWidgetController {
  public:
   // Create
   explicit DesktopBackgroundWidgetController(views::Widget* widget);
   explicit DesktopBackgroundWidgetController(ui::Layer* layer);
 
+  // When set kWindowDesktopComponent property from root window, this
+  // desctructor is called. It immediately remove the widget or layer it

[sky, 2012/08/13 17:31:05]

Move this to the class level. Also, its rather confusing. I think you mean
something like:

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 (XXX). When
the animation completes the old DesktopBackgroundWidgetController is destroyed.

[bshe, 2012/08/13 18:28:22]

Done.

+  // contains. On wallpaper change, if set property is called immediately after
+  // a new component is created. The old widget or layer will removed
+  // immediately. And a white screen will show. The new wallpaper will fade in
+  // from the white screen, which gives white flash from users' perspective.
   ~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 wrappes a DesktopBackgroundWidgetController pointer. It is used to

[sky, 2012/08/13 17:31:05]

wraps

[bshe, 2012/08/13 18:28:22]

Done.

+// save the pointer on kComponentWrapper property during the time
+// DesktopBackgroundWidgetController initialized and wallpaper animation
+// finished. After animation finished, the pointer in this class is set as
+// kWindowDesktopComponent property. If we set the pointer immediately after it
+// is created, a white flash will appear when changing wallpaper as described
+// in the comment for ~DesktopBackgroundWidgetController.
+class ComponentWrapper {
+ public:
+  explicit ComponentWrapper(
+      DesktopBackgroundWidgetController* component);
+  ~ComponentWrapper() {}
+  DesktopBackgroundWidgetController* component() { return component_; }
+
+ private:
+  DesktopBackgroundWidgetController* component_;
+  DISALLOW_COPY_AND_ASSIGN(ComponentWrapper);

[sky, 2012/08/13 17:31:05]

nit: newline between 67/68.

[bshe, 2012/08/13 18:28:22]

Done.

+};
+
 // 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_