Naive fix of a call on a nil object in CompositedLayerMapping::containingSquashedLayer.

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

 /*
  * Copyright (C) 2009, 2010, 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 2592 matching lines @@
       enclosingIntRect(LayoutRect(
           r.location() + m_owningLayer.subpixelAccumulation(), r.size())),
       invalidationReason, client};
   ApplyToGraphicsLayers(this, functor, ApplyToScrollingContentLayers);
 }
 
 const GraphicsLayerPaintInfo* CompositedLayerMapping::containingSquashedLayer(
     const LayoutObject* layoutObject,
     const Vector<GraphicsLayerPaintInfo>& layers,
     unsigned maxSquashedLayerIndex) {
+  if (!layoutObject)
+    return nullptr;
   for (size_t i = 0; i < layers.size() && i < maxSquashedLayerIndex; ++i) {
     if (layoutObject->isDescendantOf(layers[i].paintLayer->layoutObject()))
       return &layers[i];
   }
   return nullptr;
 }
 
 const GraphicsLayerPaintInfo* CompositedLayerMapping::containingSquashedLayer(
     const LayoutObject* layoutObject,
     unsigned maxSquashedLayerIndex) {
@@ skipping 626 matching lines @@
   } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
     name = "Scrolling Contents Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink