Revert 156318 - I had originally tried to build upon http://codereview.chromium.org/10869066/, but …

ui/compositor/layer_animator.h

Index: ui/compositor/layer_animator.h
===================================================================
--- ui/compositor/layer_animator.h	(revision 157564)
+++ ui/compositor/layer_animator.h	(working copy)
@@ -34,14 +34,8 @@
 // When a property of layer needs to be changed it is set by way of
 // LayerAnimator. This enables LayerAnimator to animate property changes.
 // NB: during many tests, set_disable_animations_for_test is used and causes
-// all animations to complete immediately. The layer animation is ref counted
-// so that if its owning layer is deleted (and the owning layer is only other
-// class that should ever hold a ref ptr to a LayerAnimator), the animator can
-// ensure that it is not disposed of until it finishes executing. It does this
-// by holding a reference to itself for the duration of methods for which it
-// must guarantee that |this| is valid.
-class COMPOSITOR_EXPORT LayerAnimator
-    : public AnimationContainerElement, public base::RefCounted<LayerAnimator> {
+// all animations to complete immediately.
+class COMPOSITOR_EXPORT LayerAnimator : public AnimationContainerElement {
  public:
   enum PreemptionStrategy {
     IMMEDIATELY_SET_NEW_TARGET,
@@ -52,6 +46,7 @@
   };
 
   explicit LayerAnimator(base::TimeDelta transition_duration);
+  virtual ~LayerAnimator();
 
   // No implicit animations when properties are set.
   static LayerAnimator* CreateDefaultAnimator();
@@ -84,9 +79,7 @@
   float GetTargetGrayscale() const;
 
   // Sets the layer animation delegate the animator is associated with. The
-  // animator does not own the delegate. The layer animator expects a non-NULL
-  // delegate for most of its operations, so do not call any methods without
-  // a valid delegate installed.
+  // animator does not own the delegate.
   void SetDelegate(LayerAnimationDelegate* delegate);
 
   // Sets the animation preemption strategy. This determines the behaviour if
@@ -181,22 +174,27 @@
   }
 
  protected:
-  virtual ~LayerAnimator();
-
   LayerAnimationDelegate* delegate() { return delegate_; }
   const LayerAnimationDelegate* delegate() const { return delegate_; }
 
   // Virtual for testing.
-  virtual void ProgressAnimation(LayerAnimationSequence* sequence,
+  virtual bool ProgressAnimation(LayerAnimationSequence* sequence,
                                  base::TimeDelta delta);
 
   // Returns true if the sequence is owned by this animator.
   bool HasAnimation(LayerAnimationSequence* sequence) const;
 
  private:
-  friend class base::RefCounted<LayerAnimator>;
   friend class ScopedLayerAnimationSettings;
 
+  class DestroyedTracker;
+
+  // Used by FinishAnimation() to indicate if this has been destroyed.
+  enum DestroyedType {
+    DESTROYED,
+    NOT_DESTROYED,
+  };
+
   // We need to keep track of the start time of every running animation.
   struct RunningAnimation {
     RunningAnimation(LayerAnimationSequence* sequence,
@@ -226,7 +224,8 @@
       LayerAnimationSequence* sequence) WARN_UNUSED_RESULT;
 
   // Progresses to the end of the sequence before removing it.
-  void FinishAnimation(LayerAnimationSequence* sequence);
+  DestroyedType FinishAnimation(
+      LayerAnimationSequence* sequence) WARN_UNUSED_RESULT;
 
   // Finishes any running animation with zero duration.
   void FinishAnyAnimationWithZeroDuration();
@@ -283,10 +282,6 @@
   // animation mode if set.
   base::TimeDelta GetTransitionDuration() const;
 
-  // Clears the animation queues and notifies any running animations that they
-  // have been aborted.
-  void ClearAnimationsInternal();
-
   // This is the queue of animations to run.
   AnimationQueue animation_queue_;
 
@@ -328,6 +323,8 @@
   // aborted.
   ObserverList<LayerAnimationObserver> observers_;
 
+  scoped_refptr<DestroyedTracker> destroyed_tracker_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerAnimator);
 };