Fix pixel snapping issues when layers become composited

Source/core/rendering/FilterEffectRenderer.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 347 matching lines @@
     return LayoutRect(rectForRepaint);
 }
 
 bool FilterEffectRendererHelper::prepareFilterEffect(RenderLayer* renderLayer, const LayoutRect& filterBoxRect, const LayoutRect& dirtyRect, const LayoutRect& layerRepaintRect)
 {
     ASSERT(m_haveFilterEffect && renderLayer->filterRenderer());
     m_renderLayer = renderLayer;
     m_repaintRect = dirtyRect;
 
     FilterEffectRenderer* filter = renderLayer->filterRenderer();
-    LayoutRect filterSourceRect = filter->computeSourceImageRectForDirtyRect(filterBoxRect, dirtyRect);
+    IntRect filterSourceRect = pixelSnappedIntRect(filter->computeSourceImageRectForDirtyRect(filterBoxRect, dirtyRect));
 
     if (filterSourceRect.isEmpty()) {
         // The dirty rect is not in view, just bail out.
         m_haveFilterEffect = false;
         return false;
     }
 
     // Get the zoom factor to scale the filterSourceRect input
     const RenderLayerModelObject* renderer = renderLayer->renderer();
     const RenderStyle* style = renderer ? renderer->style() : 0;
@@ skipping 57 matching lines @@
     // Get the filtered output and draw it in place.
     m_savedGraphicsContext->drawImageBuffer(filter->output(), filter->outputRect(), CompositeSourceOver);
 
     filter->clearIntermediateResults();
 
     return m_savedGraphicsContext;
 }
 
 } // namespace WebCore