CC Animations: Port Impl-only-scrolling to use compositor animation timelines.

cc/trees/layer_tree_mutators_client.h

Index: cc/trees/layer_tree_mutators_client.h
diff --git a/cc/trees/layer_tree_mutators_client.h b/cc/trees/layer_tree_mutators_client.h
index 9701e2036672dce091ee5f723b3a654d929345e5..a90ce53cd328b88795ea627bf308379e6c2aa090 100644
--- a/cc/trees/layer_tree_mutators_client.h
+++ b/cc/trees/layer_tree_mutators_client.h
@@ -34,6 +34,9 @@ class LayerTreeMutatorsClient {
       int layer_id,
       bool active_tree,
       const gfx::ScrollOffset& scroll_offset) = 0;
+
+  virtual void ScrollOffsetAnimationFinished() {}
+  virtual gfx::ScrollOffset GetScrollOffsetForAnimation(int layer_id) const = 0;
 };
 
 }  // namespace cc