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

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 8a6f270b9e6b1ede3cd1668268d2fb2e8b36b977..4f38352f9c69f2129e4d9ebe9c39c47fc4272753 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -339,6 +339,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
       int layer_id,
       LayerTreeType tree_type,
       const gfx::ScrollOffset& scroll_offset) override;
+  void ScrollOffsetAnimationFinished() override {}
+  gfx::ScrollOffset GetScrollOffsetForAnimation(int layer_id) const override;
 
   bool ScrollOffsetAnimationWasInterrupted(const Layer* layer) const;
   bool IsAnimatingFilterProperty(const Layer* layer) const;