cc: Make LayerAnimationController keep state for clearing scroll delta

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 d776ee9cbd7de72e27eca1722cf6dcfd75ca797a..48c3bdcaede9b1d330ec21beb0ae7cc1eafc289a 100644
--- a/cc/animation/layer_animation_controller.h
+++ b/cc/animation/layer_animation_controller.h
@@ -139,6 +139,17 @@ class CC_EXPORT LayerAnimationController
   // be computed.
   bool MaximumTargetScale(float* max_scale) const;
 
+  // When a scroll animation is removed on the main thread, its compositor
+  // thread counterpart continues producing scroll deltas until activation.
+  // These scroll deltas need to be cleared at activation, so that the active
+  // layer's scroll offset matches the offset provided by the main thread
+  // rather than a combination of this offset and scroll deltas produced by
+  // the removed animation. This is to provide the illusion of synchronicity to
+  // JS that simultaneously removes an animation and sets the scroll offset.
+  bool scroll_offset_animation_was_interrupted() const {
+    return scroll_offset_animation_was_interrupted_;
+  }
+
   bool needs_to_start_animations_for_testing() {
     return needs_to_start_animations_;
   }
@@ -156,8 +167,7 @@ class CC_EXPORT LayerAnimationController
       LayerAnimationController* controller_impl) const;
   void RemoveAnimationsCompletedOnMainThread(
       LayerAnimationController* controller_impl) const;
-  void PushPropertiesToImplThread(
-      LayerAnimationController* controller_impl) const;
+  void PushPropertiesToImplThread(LayerAnimationController* controller_impl);
 
   void StartAnimations(base::TimeTicks monotonic_time);
   void PromoteStartedAnimations(base::TimeTicks monotonic_time,
@@ -191,8 +201,6 @@ class CC_EXPORT LayerAnimationController
 
   void NotifyObserversAnimationWaitingForDeletion();
 
-  void NotifyObserversScrollOffsetAnimationRemoved();
-
   bool HasValueObserver();
   bool HasActiveValueObserver();
 
@@ -216,6 +224,8 @@ class CC_EXPORT LayerAnimationController
   // previous attempt at starting animations failed to start all animations.
   bool needs_to_start_animations_;
 
+  bool scroll_offset_animation_was_interrupted_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerAnimationController);
 };