Fix crash on ASSERT when in subtree layout and LayoutState is not initialized

Source/core/frame/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 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
@@ skipping 286 matching lines @@
     // DEPRECATED: Use viewportConstrainedVisibleContentRect() instead.
     IntSize scrollOffsetForFixedPosition() const;
 
     PartialLayoutState& partialLayout() { return m_partialLayout; }
 
     // Override scrollbar notifications to update the AXObject cache.
     virtual void didAddScrollbar(Scrollbar*, ScrollbarOrientation) OVERRIDE;
     virtual void willRemoveScrollbar(Scrollbar*, ScrollbarOrientation) OVERRIDE;
 
     virtual bool shouldAttemptToScrollUsingFastPath() const OVERRIDE;
+    // FIXME: This should probably be renamed as the 'inSubtreeLayout' parameter
+    // passed around the FrameView layout methods can be true while this returns
+    // false.
     bool isSubtreeLayout() const { return !!m_layoutSubtreeRoot; }
 
 protected:
     virtual bool scrollContentsFastPath(const IntSize& scrollDelta, const IntRect& rectToScroll, const IntRect& clipRect) OVERRIDE;
     virtual void scrollContentsSlowPath(const IntRect& updateRect) OVERRIDE;
 
     virtual bool isVerticalDocument() const OVERRIDE;
     virtual bool isFlippedDocument() const OVERRIDE;
 
 private:
@@ skipping 230 matching lines @@
         m_view->setCanRepaintDuringPerformLayout(m_originalValue);
     }
 private:
     FrameView* m_view;
     bool m_originalValue;
 };
 
 } // namespace WebCore
 
 #endif // FrameView_h