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

Source/core/layout/ClipRectsCache.h

 // 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.
 
 #ifndef ClipRectsCache_h
 #define ClipRectsCache_h
 
 #include "core/layout/ClipRects.h"
 
 #if ENABLE(ASSERT)
@@ skipping 17 matching lines @@
 
     NumberOfClipRectsCacheSlots,
     UncachedClipRects,
 };
 
 class ClipRectsCache {
     WTF_MAKE_FAST_ALLOCATED(ClipRectsCache);
 public:
     struct Entry {
         Entry()
-            : root(0)
+            : root(nullptr)
 #if ENABLE(ASSERT)
             , scrollbarRelevancy(IgnoreOverlayScrollbarSize)
 #endif
         {
         }
 
         const DeprecatedPaintLayer* root;
         RefPtr<ClipRects> clipRects;
 #if ENABLE(ASSERT)
         OverlayScrollbarSizeRelevancy scrollbarRelevancy;
@@ skipping 12 matching lines @@
         m_entries[slot] = Entry();
     }
 
 private:
     Entry m_entries[NumberOfClipRectsCacheSlots];
 };
 
 } // namespace blink
 
 #endif // ClipRectsCache_h