Avoid unnecessary descents into nested boxes with floats.

Source/core/rendering/RenderBlock.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 143 matching lines @@
 
 RenderBlock::RenderBlock(ContainerNode* node)
     : RenderBox(node)
     , m_lineHeight(-1)
     , m_hasMarginBeforeQuirk(false)
     , m_hasMarginAfterQuirk(false)
     , m_beingDestroyed(false)
     , m_hasMarkupTruncation(false)
     , m_hasBorderOrPaddingLogicalWidthChanged(false)
     , m_hasOnlySelfCollapsingChildren(false)
+    , m_descendantsWithFloatsMarkedForLayout(false)
 {
     setChildrenInline(true);
 }
 
 static void removeBlockFromDescendantAndContainerMaps(RenderBlock* block, TrackedDescendantsMap*& descendantMap, TrackedContainerMap*& containerMap)
 {
     if (OwnPtr<TrackedRendererListHashSet> descendantSet = descendantMap->take(block)) {
         TrackedRendererListHashSet::iterator end = descendantSet->end();
         for (TrackedRendererListHashSet::iterator descendant = descendantSet->begin(); descendant != end; ++descendant) {
             TrackedContainerMap::iterator it = containerMap->find(*descendant);
@@ skipping 4780 matching lines @@
 void RenderBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const RenderObject* obj) const
 {
     showRenderObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace WebCore