Merge 130322 - [Sub-pixel layout] incorrect rendering when painting sub-layers as their own root

Source/WebCore/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 3140 matching lines @@
                 useClipRect = !filterRenderer()->hasFilterThatMovesPixels();
             }
         }
     }
 #endif
     
     if (shouldPaintContent || shouldPaintOutline || isPaintingOverlayScrollbars) {
         calculateRects(rootLayer, region, (localPaintFlags & PaintLayerTemporaryClipRects) ? TemporaryClipRects : PaintingClipRects, paintDirtyRect, layerBounds, damageRect, clipRectToApply, outlineRect,
             IgnoreOverlayScrollbarSize, localPaintFlags & PaintLayerPaintingOverflowContents ? IgnoreOverflowClip : RespectOverflowClip);
         paintOffset = toPoint(layerBounds.location() - renderBoxLocation() + subPixelAccumulation);
+        if (this == rootLayer)
+            paintOffset = roundedIntPoint(paintOffset);
     }
 
     bool forceBlackText = paintBehavior & PaintBehaviorForceBlackText;
     bool selectionOnly  = paintBehavior & PaintBehaviorSelectionOnly;
     
     // If this layer's renderer is a child of the paintingRoot, we render unconditionally, which
     // is done by passing a nil paintingRoot down to our renderer (as if no paintingRoot was ever set).
     // Else, our renderer tree may or may not contain the painting root, so we pass that root along
     // so it will be tested against as we descend through the renderers.
     RenderObject* paintingRootForRenderer = 0;
@@ skipping 1899 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif