Reland "Avoid layout/full-repaint on view height change if possible"

Source/core/rendering/RenderView.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 189 matching lines @@
     double layoutViewportHeight() const;
 
     // Suspends the LayoutState optimization. Used under transforms that cannot be represented by
     // LayoutState (common in SVG) and when manipulating the render tree during layout in ways
     // that can trigger repaint of a non-child (e.g. when a list item moves its list marker around).
     // Note that even when disabled, LayoutState is still used to store layoutDelta.
     // These functions may only be accessed by LayoutStateMaintainer or LayoutStateDisabler.
     void disableLayoutState() { m_layoutStateDisableCount++; }
     void enableLayoutState() { ASSERT(m_layoutStateDisableCount > 0); m_layoutStateDisableCount--; }
 
+    bool trySimplifiedLayoutOnHeightChange();
+
 private:
     virtual void mapLocalToContainer(const RenderLayerModelObject* repaintContainer, TransformState&, MapCoordinatesFlags = ApplyContainerFlip, bool* wasFixed = 0) const OVERRIDE;
     virtual const RenderObject* pushMappingToContainer(const RenderLayerModelObject* ancestorToStopAt, RenderGeometryMap&) const OVERRIDE;
     virtual void mapAbsoluteToLocalPoint(MapCoordinatesFlags, TransformState&) const OVERRIDE;
     virtual void computeSelfHitTestRects(Vector<LayoutRect>&, const LayoutPoint& layerOffset) const OVERRIDE;
 
     void initializeLayoutState(LayoutState&);
 
     bool shouldRepaint(const LayoutRect&) const;
 
@@ skipping 132 matching lines @@
     {
         m_view.enableLayoutState();
     }
 private:
     RenderView& m_view;
 };
 
 } // namespace WebCore
 
 #endif // RenderView_h