[New Multicolumn] Support dynamic insertion and removal of multicol content.

Source/core/rendering/RenderMultiColumnSpannerPlaceholder.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/rendering/RenderMultiColumnSpannerPlaceholder.h"
 
 namespace blink {
 
 static void copyMarginProperties(RenderStyle* placeholderStyle, const RenderStyle* spannerStyle)
@@ skipping 16 matching lines @@
     newSpanner->setStyle(newStyle);
     return newSpanner;
 }
 
 RenderMultiColumnSpannerPlaceholder::RenderMultiColumnSpannerPlaceholder(RenderBox* rendererInFlowThread)
     : RenderBox(0)
     , m_rendererInFlowThread(rendererInFlowThread)
 {
 }
 
-void RenderMultiColumnSpannerPlaceholder::spannerWillBeRemoved()
-{
-    ASSERT(m_rendererInFlowThread);
-    RenderBox* renderer = m_rendererInFlowThread;
-    m_rendererInFlowThread = 0;
-    flowThread()->flowThreadDescendantWillBeRemoved(renderer);
-    // |this| should be destroyed by now.
-}
-
 void RenderMultiColumnSpannerPlaceholder::updateMarginProperties()
 {
     RefPtr<RenderStyle> newStyle = RenderStyle::clone(style());
     copyMarginProperties(newStyle.get(), m_rendererInFlowThread->style());
     setStyle(newStyle);
 }
 
 void RenderMultiColumnSpannerPlaceholder::willBeRemovedFromTree()
 {
     if (m_rendererInFlowThread)
@@ skipping 51 matching lines @@
 {
     return !m_rendererInFlowThread->hasSelfPaintingLayer() && m_rendererInFlowThread->nodeAtPoint(request, result, locationInContainer, accumulatedOffset, action);
 }
 
 const char* RenderMultiColumnSpannerPlaceholder::renderName() const
 {
     return "RenderMultiColumnSpannerPlaceholder";
 }
 
 }