LayoutBlock::m_descendantsWithFloatsMarkedForLayout doesn't need to be mutable.

third_party/WebKit/Source/core/layout/LayoutBlock.h

 /*
  * 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 Apple Inc. 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
  * version 2 of the License, or (at your option) any later version.
@@ skipping 482 matching lines @@
     LayoutObjectChildList m_children;
     LineBoxList m_lineBoxes; // All of the root line boxes created for this block flow.  For example, <div>Hello<br>world.</div> will have two total lines for the <div>.
 
     unsigned m_hasMarginBeforeQuirk : 1; // Note these quirk values can't be put in LayoutBlockRareData since they are set too frequently.
     unsigned m_hasMarginAfterQuirk : 1;
     unsigned m_beingDestroyed : 1;
     unsigned m_hasMarkupTruncation : 1;
     unsigned m_widthAvailableToChildrenChanged  : 1;
     unsigned m_heightAvailableToChildrenChanged  : 1;
     unsigned m_isSelfCollapsing : 1; // True if margin-before and margin-after are adjoining.
-    mutable unsigned m_descendantsWithFloatsMarkedForLayout : 1;
+    unsigned m_descendantsWithFloatsMarkedForLayout : 1;
 
     unsigned m_hasPositionedObjects : 1;
     unsigned m_hasPercentHeightDescendants : 1;
 
     // LayoutRubyBase objects need to be able to split and merge, moving their children around
     // (calling moveChildTo, moveAllChildrenTo, and makeChildrenNonInline).
     friend class LayoutRubyBase;
     // FIXME-BLOCKFLOW: Remove this when the line layout stuff has all moved out of LayoutBlock
     friend class LineBreaker;
 
     // FIXME: This is temporary as we move code that accesses block flow
     // member variables out of LayoutBlock and into LayoutBlockFlow.
     friend class LayoutBlockFlow;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBlock, isLayoutBlock());
 
 } // namespace blink
 
 #endif // LayoutBlock_h