Merge 159961 "Defer the real work in updateCompositingLayers unt..."

Source/core/rendering/CompositedLayerMapping.cpp

Index: Source/core/rendering/CompositedLayerMapping.cpp
===================================================================
--- Source/core/rendering/CompositedLayerMapping.cpp	(revision 159992)
+++ Source/core/rendering/CompositedLayerMapping.cpp	(working copy)
@@ -750,6 +750,8 @@
         }
     }
 
+    m_owningLayer->positionOverflowControls();
+
     // If this layer was created just for clipping or to apply perspective, it doesn't need its own backing store.
     setRequiresOwnBackingStore(compositor()->requiresOwnBackingStore(m_owningLayer, compAncestor));