Don't add subpixel accumulations for squashed layers when invalidating them.

Source/core/rendering/RenderLayerModelObject.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 Apple Inc. All rights reserved.
  * Copyright (C) 2010, 2012 Google 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 183 matching lines @@
 
 void RenderLayerModelObject::setBackingNeedsPaintInvalidationInRect(const LayoutRect& r, PaintInvalidationReason invalidationReason) const
 {
     // https://bugs.webkit.org/show_bug.cgi?id=61159 describes an unreproducible crash here,
     // so assert but check that the layer is composited.
     ASSERT(compositingState() != NotComposited);
 
     // FIXME: generalize accessors to backing GraphicsLayers so that this code is squashing-agnostic.
     if (layer()->groupedMapping()) {
         LayoutRect paintInvalidationRect = r;
-        paintInvalidationRect.move(layer()->subpixelAccumulation());
-        if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer())
-            squashingLayer->setNeedsDisplayInRect(pixelSnappedIntRect(paintInvalidationRect), invalidationReason);
+        if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer()) {
+            // Note: the subpixel accumulation of layer() does not need

[leviw_travelin_and_unemployed, 2014/10/14 21:49:09]

Nit: Did you not finish writing this comment?

[chrishtr, 2014/10/14 21:54:32]

Done

+            IntRect snappedRect = pixelSnappedIntRect(paintInvalidationRect);

[leviw_travelin_and_unemployed, 2014/10/14 21:49:09]

Why bother with adding the local variable?

[chrishtr, 2014/10/14 21:54:32]

Done.

+            squashingLayer->setNeedsDisplayInRect(snappedRect, invalidationReason);
+        }
     } else {
         layer()->compositedLayerMapping()->setContentsNeedDisplayInRect(r, invalidationReason);
     }
 }
 
 } // namespace blink