Replace LayerImpl::sorting_context_id with transform reference.

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index f25894d2f9ae4bb2c9517fc83fc876ad832b55f8..e42312fbcf7ea91054967070836f205d157ba516 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -1165,7 +1165,6 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
   layer->SetUseLocalTransformForBackfaceVisibility(
       use_local_transform_for_backface_visibility_);
   layer->SetShouldCheckBackfaceVisibility(should_check_backface_visibility_);
-  layer->Set3dSortingContextId(inputs_.sorting_context_id);
 
   layer->SetScrollClipLayer(inputs_.scroll_clip_layer_id);
   layer->set_user_scrollable_horizontal(inputs_.user_scrollable_horizontal);