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

Source/core/layout/LayoutMultiColumnSpannerPlaceholder.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/LayoutMultiColumnSpannerPlaceholder.h"
 
 namespace blink {
 
 static void copyMarginProperties(ComputedStyle& placeholderStyle, const ComputedStyle& spannerStyle)
@@ skipping 11 matching lines @@
     LayoutMultiColumnSpannerPlaceholder* newSpanner = new LayoutMultiColumnSpannerPlaceholder(&layoutObjectInFlowThread);
     Document& document = layoutObjectInFlowThread.document();
     newSpanner->setDocumentForAnonymous(&document);
     RefPtr<ComputedStyle> newStyle = ComputedStyle::createAnonymousStyleWithDisplay(parentStyle, BLOCK);
     copyMarginProperties(*newStyle, layoutObjectInFlowThread.styleRef());
     newSpanner->setStyle(newStyle);
     return newSpanner;
 }
 
 LayoutMultiColumnSpannerPlaceholder::LayoutMultiColumnSpannerPlaceholder(LayoutBox* layoutObjectInFlowThread)
-    : LayoutBox(0)
+    : LayoutBox(nullptr)
     , m_layoutObjectInFlowThread(layoutObjectInFlowThread)
 {
 }
 
 void LayoutMultiColumnSpannerPlaceholder::updateMarginProperties()
 {
     RefPtr<ComputedStyle> newStyle = ComputedStyle::clone(styleRef());
     copyMarginProperties(*newStyle, m_layoutObjectInFlowThread->styleRef());
     setStyle(newStyle);
 }
@@ skipping 60 matching lines @@
     if (!m_layoutObjectInFlowThread->hasSelfPaintingLayer())
         m_layoutObjectInFlowThread->paint(paintInfo, paintOffset);
 }
 
 bool LayoutMultiColumnSpannerPlaceholder::nodeAtPoint(HitTestResult& result, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction action)
 {
     return !m_layoutObjectInFlowThread->hasSelfPaintingLayer() && m_layoutObjectInFlowThread->nodeAtPoint(result, locationInContainer, accumulatedOffset, action);
 }
 
 }