Fix white flash when user sings out and wallpaper animation regression

ash/desktop_background/desktop_background_widget_controller.h

Index: ash/desktop_background/desktop_background_widget_controller.h
diff --git a/ash/desktop_background/desktop_background_widget_controller.h b/ash/desktop_background/desktop_background_widget_controller.h
index fe07ef30430b656ed0ad7f90537e09f5de62b491..a43db147111637799c24df73bc4f8ed06a51f569 100644
--- a/ash/desktop_background/desktop_background_widget_controller.h
+++ b/ash/desktop_background/desktop_background_widget_controller.h
@@ -21,6 +21,12 @@ class DesktopBackgroundWidgetController {
   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.
@@ -43,11 +49,32 @@ class DesktopBackgroundWidgetController {
   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