Don't call RenderObject::enclosingLayer on a null pointer

Source/core/page/scrolling/ScrollingCoordinator.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 376 matching lines @@
 // In order to do a DFS cross-frame walk of the RenderLayer tree, we need to know which
 // RenderLayers have child frames inside of them. This computes a mapping for the
 // current frame which we can consult while walking the layers of that frame.
 // Whenever we descend into a new frame, a new map will be created.
 typedef HashMap<const RenderLayer*, Vector<const LocalFrame*> > LayerFrameMap;
 static void makeLayerChildFrameMap(const LocalFrame* currentFrame, LayerFrameMap* map)
 {
     map->clear();
     const FrameTree& tree = currentFrame->tree();
     for (const LocalFrame* child = tree.firstChild(); child; child = child->tree().nextSibling()) {
-        if (const RenderLayer* containingLayer = child->ownerRenderer()->enclosingLayer()) {
-            LayerFrameMap::iterator iter = map->find(containingLayer);
-            if (iter == map->end())
-                map->add(containingLayer, Vector<const LocalFrame*>()).storedValue->value.append(child);
-            else
-                iter->value.append(child);
-        }
+        const RenderObject* ownerRenderer = child->ownerRenderer();
+        if (!ownerRenderer)
+            continue;
+        const RenderLayer* containingLayer = ownerRenderer->enclosingLayer();
+        LayerFrameMap::iterator iter = map->find(containingLayer);
+        if (iter == map->end())
+            map->add(containingLayer, Vector<const LocalFrame*>()).storedValue->value.append(child);
+        else
+            iter->value.append(child);
     }
 }
 
 static void convertLayerRectsToEnclosingCompositedLayerRecursive(
     const RenderLayer* curLayer,
     const LayerHitTestRects& layerRects,
     LayerHitTestRects& compositorRects,
     RenderGeometryMap& geometryMap,
     HashSet<const RenderLayer*>& layersWithRects,
     LayerFrameMap& layerChildFrameMap)
@@ skipping 540 matching lines @@
     bool frameIsScrollable = frameView && frameView->isScrollable();
     if (frameIsScrollable != m_wasFrameScrollable)
         return true;
 
     if (WebLayer* scrollLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : 0)
         return blink::WebSize(frameView->contentsSize()) != scrollLayer->bounds();
     return false;
 }
 
 } // namespace WebCore