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

Source/core/layout/LayoutFlowThread.cpp

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. 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.
@@ skipping 19 matching lines @@
 #include "config.h"
 
 #include "core/layout/LayoutFlowThread.h"
 
 #include "core/layout/LayoutMultiColumnSet.h"
 #include "core/layout/LayoutView.h"
 
 namespace blink {
 
 LayoutFlowThread::LayoutFlowThread()
-    : LayoutBlockFlow(0)
+    : LayoutBlockFlow(nullptr)
     , m_columnSetsInvalidated(false)
     , m_columnSetsHaveUniformLogicalHeight(true)
     , m_pageLogicalSizeChanged(false)
 {
 }
 
 void LayoutFlowThread::removeColumnSetFromThread(LayoutMultiColumnSet* columnSet)
 {
     ASSERT(columnSet);
     m_multiColumnSetList.remove(columnSet);
@@ skipping 144 matching lines @@
 
 void LayoutFlowThread::MultiColumnSetSearchAdapter::collectIfNeeded(const MultiColumnSetInterval& interval)
 {
     if (m_result)
         return;
     if (interval.low() <= m_offset && interval.high() > m_offset)
         m_result = interval.data();
 }
 
 } // namespace blink