Made layout viewport scroll updates from compositor work like ordinary layers.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index cc98d5d17dd84cd22aaced710af228ea584e4b8b..3be80e8b792708dd0164fc8409527b75bad86dad 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3366,8 +3366,13 @@ static void CollectScrollDeltas(ScrollAndScaleSet* scroll_info,
   if (tree_impl->LayerListIsEmpty())
     return;
 
+  int inner_viewport_layer_id =
+      tree_impl->InnerViewportScrollLayer()
+          ? tree_impl->InnerViewportScrollLayer()->id()
+          : Layer::INVALID_ID;
+
   return tree_impl->property_trees()->scroll_tree.CollectScrollDeltas(
-      scroll_info);
+      scroll_info, inner_viewport_layer_id);
 }
 
 std::unique_ptr<ScrollAndScaleSet> LayerTreeHostImpl::ProcessScrollDeltas() {