Added a CallbackLayerAnimationObserver.

ui/compositor/layer_animation_observer.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 UI_COMPOSITOR_LAYER_ANIMATION_OBSERVER_H_
 #define UI_COMPOSITOR_LAYER_ANIMATION_OBSERVER_H_
 
 #include <map>
 #include <set>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/compositor/compositor_export.h"
 #include "ui/compositor/layer_animation_element.h"
 
 namespace ui {
 
+namespace test {
+class LayerAnimationObserverTestApi;
+}  // namespace test
+
 class LayerAnimationSequence;
 class ScopedLayerAnimationSettings;
 class ImplicitAnimationObserver;
 
 // LayerAnimationObservers are notified when animations complete.
 class COMPOSITOR_EXPORT LayerAnimationObserver  {
  public:
   // Called when the |sequence| starts.
   virtual void OnLayerAnimationStarted(LayerAnimationSequence* sequence);
 
@@ skipping 11 matching lines @@
       LayerAnimationSequence* sequence) = 0;
 
  protected:
   typedef std::set<LayerAnimationSequence*> AttachedSequences;
 
   LayerAnimationObserver();
   virtual ~LayerAnimationObserver();
 
   // If the animator is destroyed during an animation, the animations are
   // aborted. The resulting NotifyAborted notifications will NOT be sent to
-  // this observer if this function returns false. NOTE: IF YOU override THIS
-  // FUNCTION TO RETURN TRUE, YOU MUST REMEMBER TO REMOVE YOURSELF AS AN
-  // OBSERVER WHEN YOU ARE DESTROYED.
+  // this observer if this function returns false. An observer who wants to
+  // receive the NotifyAborted notifications during destruction can override
+  // this function to return true.
+  //
+  // *** IMPORTANT ***: If you override this function to return true AND you are
+  // using the pattern described below, then make sure you explicity remove
+  // yourself as an observer before the animator is destroyed!
+  //
+  // This opt-in pattern is used because it is a common pattern for a class to
+  // be the observer of an animation that it itself owns. In such a case the
+  // animator will be destroyed as the owning class is destructed and we don't
+  // want the NotifyAbort being invoked on a partially destroyed observer.
   virtual bool RequiresNotificationWhenAnimatorDestroyed() const;
 
   // Called when |this| is added to |sequence|'s observer list.
   virtual void OnAttachedToSequence(LayerAnimationSequence* sequence);
 
   // Called when |this| is removed to |sequence|'s observer list.
   virtual void OnDetachedFromSequence(LayerAnimationSequence* sequence);
 
   // Detaches this observer from all sequences it is currently observing.
   void StopObserving();
 
   const AttachedSequences& attached_sequences() const {
     return attached_sequences_;
   }
 
  private:
   friend class LayerAnimationSequence;
+  friend class test::LayerAnimationObserverTestApi;
 
   // Called when |this| is added to |sequence|'s observer list.
   void AttachedToSequence(LayerAnimationSequence* sequence);
 
   // Called when |this| is removed to |sequence|'s observer list.
   // This will only result in notifications if |send_notification| is true.
   void DetachedFromSequence(LayerAnimationSequence* sequence,
                             bool send_notification);
 
   AttachedSequences attached_sequences_;
@@ skipping 67 matching lines @@
                    AnimationStatus> PropertyAnimationStatusMap;
   PropertyAnimationStatusMap property_animation_status_;
 
   // True if OnLayerAnimationScheduled() has been called at least once.
   bool first_sequence_scheduled_;
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_LAYER_ANIMATION_OBSERVER_H_