Keep track of multiple layout roots

Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 1932 matching lines @@
     computedValues.m_position = logicalLeft();
     computedValues.m_margins.m_start = marginStart();
     computedValues.m_margins.m_end = marginEnd();
 
     if (isOutOfFlowPositioned()) {
         computePositionedLogicalWidth(computedValues);
         return;
     }
 
     // If layout is limited to a subtree, the subtree root's logical width does not change.
-    if (node() && view()->frameView() && view()->frameView()->layoutRoot(true) == this)
+    if (node() && view()->frameView() && view()->frameView()->isLayoutRoot(*this))
         return;
 
     // The parent box is flexing us, so it has increased or decreased our
     // width.  Use the width from the style context.
     // FIXME: Account for writing-mode in flexible boxes.
     // https://bugs.webkit.org/show_bug.cgi?id=46418
     if (hasOverrideWidth() && parent()->isFlexibleBoxIncludingDeprecated()) {
         computedValues.m_extent = overrideLogicalContentWidth() + borderAndPaddingLogicalWidth();
         return;
     }
@@ skipping 2663 matching lines @@
 }
 
 void LayoutBox::invalidateDisplayItemClients(DisplayItemList* displayItemList) const
 {
     LayoutBoxModelObject::invalidateDisplayItemClients(displayItemList);
     if (LayerScrollableArea* area = scrollableArea())
         displayItemList->invalidate(area->displayItemClient());
 }
 
 } // namespace blink