aura: Some changes in Window and Desktop.

ui/aura/desktop.h

Index: ui/aura/desktop.h
diff --git a/ui/aura/desktop.h b/ui/aura/desktop.h
index 521876a273e99f7a1d353e75d33d505681d616d6..9cb7c18ca70bffae25161930f8cb08b39b471f52 100644
--- a/ui/aura/desktop.h
+++ b/ui/aura/desktop.h
@@ -31,6 +31,12 @@ class MouseEvent;
 // Desktop is responsible for hosting a set of windows.
 class AURA_EXPORT Desktop : public ui::CompositorDelegate {
  public:
+  // Observers can listen to various events on the Desktop.
+  class Observer {
+   public:
+    virtual void OnDesktopResized(const gfx::Size& new_size) {}

[sky, 2011/10/12 21:11:27]

I think we should make these pure virtual. Also, add a protected virtual
destructor and move this into its own header.

[sadrul, 2011/10/12 21:33:23]

Done. I kept the empty implementation for WindowObserver: an observer may only
be interested in one particular event, so it shouldn't be forced to provide
implementations for all the possible events.

+  };
+
   Desktop();
   virtual ~Desktop();
 
@@ -100,6 +106,11 @@ class AURA_EXPORT Desktop : public ui::CompositorDelegate {
   // It must never be stored.
   MessageLoop::Dispatcher* GetDispatcher();
 
+  // Add/remove observer.
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+  bool HasObserver(Observer* observer);

[sky, 2011/10/12 21:11:27]

Unless we need HasObserver, don't add it.

[sadrul, 2011/10/12 21:33:23]

It's not needed right now. Removed.

+
   static Desktop* GetInstance();
 
  private:
@@ -128,6 +139,8 @@ class AURA_EXPORT Desktop : public ui::CompositorDelegate {
   // destruction.
   bool in_destructor_;
 
+  ObserverList<Observer> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(Desktop);
 };