cc: Support animating scroll offset

cc/animation/layer_animation_controller.h

Index: cc/animation/layer_animation_controller.h
diff --git a/cc/animation/layer_animation_controller.h b/cc/animation/layer_animation_controller.h
index 705fd7f059bc0b756d4ccf35c82a0ba49253dd8a..564a5933e7f70fb400c200f8aba812c42f5f3604 100644
--- a/cc/animation/layer_animation_controller.h
+++ b/cc/animation/layer_animation_controller.h
@@ -30,6 +30,7 @@ class AnimationRegistrar;
 class FilterOperations;
 class KeyframeValueList;
 class LayerAnimationValueObserver;
+class LayerAnimationValueProvider;
 
 class CC_EXPORT LayerAnimationController
     : public base::RefCounted<LayerAnimationController> {
@@ -95,6 +96,15 @@ class CC_EXPORT LayerAnimationController
   void AddEventObserver(LayerAnimationEventObserver* observer);
   void RemoveEventObserver(LayerAnimationEventObserver* observer);
 
+  void set_value_provider(LayerAnimationValueProvider* provider) {
+    value_provider_ = provider;
+  }
+
+  void remove_value_provider(LayerAnimationValueProvider* provider) {

[Ian Vollick, 2013/11/29 15:29:29]

Why not just set_value_provider(NULL)?

[ajuma, 2013/11/29 21:18:41]

The issue is that a LayerImpl might not know whether it's the value provider for
its LayerAnimationController. Only active layers act as value providers.
LayerImpl checks IsActive before setting itself up as a value provider. Doing
the same thing for de-registering seems more fragile, since IsActive works by
checking if the LayerImpl's tree is the same as LayerTreeHostImpl's active_tree.
If, in the future, we allowed a LayerTreeHostImpl to throw away its active tree
and create a  new one, and if the old active tree's destruction sequence
happened after LayerTreeHostImpl's active tree pointer had been reset, relying
on the IsActive check when destroying would lead to incorrect behavior here.

[Ian Vollick, 2013/12/02 21:23:32]

Thanks for the explanation.

+    if (value_provider_ == provider)
+      value_provider_ = NULL;
+  }
+
   void set_layer_animation_delegate(AnimationDelegate* delegate) {
     layer_animation_delegate_ = delegate;
   }
@@ -136,6 +146,7 @@ class CC_EXPORT LayerAnimationController
   void NotifyObserversOpacityAnimated(float opacity);
   void NotifyObserversTransformAnimated(const gfx::Transform& transform);
   void NotifyObserversFilterAnimated(const FilterOperations& filter);
+  void NotifyObserversScrollOffsetAnimated(gfx::Vector2dF scroll_offset);
 
   void NotifyObserversAnimationWaitingForDeletion();
 
@@ -154,6 +165,8 @@ class CC_EXPORT LayerAnimationController
   ObserverList<LayerAnimationValueObserver> value_observers_;
   ObserverList<LayerAnimationEventObserver> event_observers_;
 
+  LayerAnimationValueProvider* value_provider_;
+
   AnimationDelegate* layer_animation_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerAnimationController);