Replace LayerImpl::sorting_context_id with transform reference.

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp

Index: third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
index b0b7bf100fa42a7e787e623677c90f0132750b92..80b099fa10c2bdf5bce662d720129448ea8dd3f0 100644
--- a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
+++ b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
@@ -1211,12 +1211,6 @@ void PaintArtifactCompositor::update(
     layer->SetEffectTreeIndex(effectId);
     layer->SetScrollTreeIndex(scrollId);
 
-    // TODO(jbroman): This probably shouldn't be necessary, but it is still
-    // queried by RenderSurfaceImpl.
-    layer->Set3dSortingContextId(layerTree->property_trees()
-                                     ->transform_tree.Node(transformId)
-                                     ->sorting_context_id);
-
     layer->SetShouldCheckBackfaceVisibility(pendingLayer.backfaceHidden);
 
     if (m_extraDataForTestingEnabled)