Change PaintLayer::m_layoutObject to a reference.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
index 2ad2bf633fe8be81fc7b062c3de33ed12223218d..0dda1a4a9cd0574022b3d81de5e482a3f2acfcd5 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
@@ -376,7 +376,7 @@ class CORE_EXPORT CompositedLayerMapping final : public GraphicsLayerClient {
                                     bool needsLayer,
                                     CompositingReasons);
 
-  LayoutBoxModelObject* layoutObject() const {
+  LayoutBoxModelObject& layoutObject() const {
     return m_owningLayer.layoutObject();
   }
   PaintLayerCompositor* compositor() const {
@@ -489,8 +489,9 @@ class CORE_EXPORT CompositedLayerMapping final : public GraphicsLayerClient {
   // the child is not clipped. We accept the approximation because most border
   // radii are small and the outcome is used to reduce the number of layers,
   // not influence correctness.
-  bool ancestorRoundedCornersWontClip(const LayoutObject* child,
-                                      const LayoutObject* clippingAncestor);
+  bool ancestorRoundedCornersWontClip(
+      const LayoutBoxModelObject& child,
+      const LayoutBoxModelObject& clippingAncestor);
 
   // Return true in |owningLayerIsClipped| iff |m_owningLayer|'s compositing
   // ancestor is not a descendant (inclusive) of the clipping container for