C++11: Replace 0 with nullptr where applicable in layout code.

Source/core/layout/compositing/CompositingInputsUpdater.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/layout/compositing/CompositingInputsUpdater.h"
 
 #include "core/layout/LayoutBlock.h"
 #include "core/layout/compositing/CompositedDeprecatedPaintLayerMapping.h"
 #include "core/layout/compositing/DeprecatedPaintLayerCompositor.h"
@@ skipping 41 matching lines @@
         } else {
             current = current->containingBlock();
         }
 
         if (current->hasLayer())
             return static_cast<const LayoutBoxModelObject*>(current)->layer();
         // Having clip or overflow clip forces the LayoutObject to become a layer.
         ASSERT(!current->hasClipOrOverflowClip());
     }
     ASSERT_NOT_REACHED();
-    return 0;
+    return nullptr;
 }
 
 static const DeprecatedPaintLayer* findParentLayerOnContainingBlockChain(const LayoutObject* object)
 {
     for (const LayoutObject* current = object; current; current = current->containingBlock()) {
         if (current->hasLayer())
             return static_cast<const LayoutBoxModelObject*>(current)->layer();
     }
     ASSERT_NOT_REACHED();
-    return 0;
+    return nullptr;
 }
 
 static bool hasClippedStackingAncestor(const DeprecatedPaintLayer* layer, const DeprecatedPaintLayer* clippingLayer)
 {
     if (layer == clippingLayer)
         return false;
     const LayoutObject* clippingLayoutObject = clippingLayer->layoutObject();
     for (const DeprecatedPaintLayer* current = layer->compositingContainer(); current && current != clippingLayer; current = current->compositingContainer()) {
         if (current->layoutObject()->hasClipOrOverflowClip() && !clippingLayoutObject->isDescendantOf(current->layoutObject()))
             return true;
@@ skipping 105 matching lines @@
     ASSERT(!layer->childNeedsCompositingInputsUpdate());
     ASSERT(!layer->needsCompositingInputsUpdate());
 
     for (DeprecatedPaintLayer* child = layer->firstChild(); child; child = child->nextSibling())
         assertNeedsCompositingInputsUpdateBitsCleared(child);
 }
 
 #endif
 
 } // namespace blink