Don't always full invalidation on 'position' style change

Source/core/rendering/style/RenderStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 525 matching lines @@
         || inherited_flags._text_transform != other.inherited_flags._text_transform
         || inherited_flags._direction != other.inherited_flags._direction
         || inherited_flags._white_space != other.inherited_flags._white_space
         || inherited_flags.m_writingMode != other.inherited_flags.m_writingMode)
         return true;
 
     if (noninherited_flags.overflowX != other.noninherited_flags.overflowX
         || noninherited_flags.overflowY != other.noninherited_flags.overflowY
         || noninherited_flags.clear != other.noninherited_flags.clear
         || noninherited_flags.unicodeBidi != other.noninherited_flags.unicodeBidi
-        || noninherited_flags.position != other.noninherited_flags.position
         || noninherited_flags.floating != other.noninherited_flags.floating
         || noninherited_flags.originalDisplay != other.noninherited_flags.originalDisplay)
         return true;
 
     if (noninherited_flags.effectiveDisplay >= FIRST_TABLE_DISPLAY && noninherited_flags.effectiveDisplay <= LAST_TABLE_DISPLAY) {
         if (inherited_flags._border_collapse != other.inherited_flags._border_collapse
             || inherited_flags._empty_cells != other.inherited_flags._empty_cells
             || inherited_flags._caption_side != other.inherited_flags._caption_side
             || noninherited_flags.tableLayout != other.noninherited_flags.tableLayout)
             return true;
@@ skipping 40 matching lines @@
             || m_box->maxHeight() != other.m_box->maxHeight())
             return true;
 
         if (m_box->verticalAlign() != other.m_box->verticalAlign())
             return true;
 
         if (m_box->boxSizing() != other.m_box->boxSizing())
             return true;
     }
 
-    if (noninherited_flags.verticalAlign != other.noninherited_flags.verticalAlign)
+    if (noninherited_flags.verticalAlign != other.noninherited_flags.verticalAlign
+        || noninherited_flags.position != other.noninherited_flags.position)
         return true;
 
     if (surround.get() != other.surround.get()) {
         if (surround->margin != other.surround->margin)
             return true;
 
         if (surround->padding != other.surround->padding)
             return true;
     }
 
@@ skipping 1077 matching lines @@
     // right
     radiiSum = radii.topRight().height() + radii.bottomRight().height();
     if (radiiSum > rect.height())
         factor = std::min(rect.height() / radiiSum, factor);
 
     ASSERT(factor <= 1);
     return factor;
 }
 
 } // namespace blink