[repaint-after-layout] Skip full repaint if the style difference is layout.

Source/core/rendering/RenderBox.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 127 matching lines @@
 }
 
 void RenderBox::styleWillChange(StyleDifference diff, const RenderStyle* newStyle)
 {
     RenderStyle* oldStyle = style();
     if (oldStyle) {
         // The background of the root element or the body element could propagate up to
         // the canvas.  Just dirty the entire canvas when our style changes substantially.
         if (diff >= StyleDifferenceRepaint && node() &&
             (isHTMLHtmlElement(*node()) || isHTMLBodyElement(*node()))) {
-            view()->repaint();
+
+            if (!RuntimeEnabledFeatures::repaintAfterLayoutEnabled() || diff != StyleDifferenceLayout)
+                view()->repaint();
 
             if (oldStyle->hasEntirelyFixedBackground() != newStyle->hasEntirelyFixedBackground())
                 view()->compositor()->rootFixedBackgroundsChanged();
         }
 
         // When a layout hint happens and an object's position style changes, we have to do a layout
         // to dirty the render tree using the old position value now.
         if (diff == StyleDifferenceLayout && parent() && oldStyle->position() != newStyle->position()) {
             markContainingBlocksForLayout();
             if (oldStyle->position() == StaticPosition)
@@ skipping 4531 matching lines @@
         return 0;
 
     if (!layoutState && !flowThreadContainingBlock())
         return 0;
 
     RenderBlock* containerBlock = containingBlock();
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
 } // namespace WebCore