Use enclosingIntRect when computing paint invalidations across transforms.

third_party/WebKit/Source/core/layout/LayoutBox.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 2087 matching lines @@
         if (container->styleRef().isFlippedBlocksWritingMode())
             rect.setX(m_frameRect.width() - rect.maxX());
     }
 
     LayoutPoint topLeft = rect.location();
     topLeft.move(locationOffset());
 
     // We are now in our parent container's coordinate space.  Apply our transform to obtain a bounding box
     // in the parent's coordinate space that encloses us.
     if (hasLayer() && layer()->transform()) {
-        rect = LayoutRect(layer()->transform()->mapRect(pixelSnappedIntRect(rect)));
+        // Use enclosingIntRect because we cannot properly compute pixel snapping for painted elements within
+        // the transform since we don't know the desired subpixel accumulation at this point, and the transform may
+        // include a scale.
+        rect = LayoutRect(layer()->transform()->mapRect(enclosingIntRect(rect)));
         topLeft = rect.location();
         topLeft.move(locationOffset());
     }
 
     const ComputedStyle& styleToUse = styleRef();
     EPosition position = styleToUse.position();
     if (position == AbsolutePosition && container->isInFlowPositioned() && container->isLayoutInline()) {
         topLeft += toLayoutInline(container)->offsetForInFlowPositionedInline(*this);
     } else if (styleToUse.hasInFlowPosition() && layer()) {
         // Apply the relative position offset when invalidating a rectangle.  The layer
@@ skipping 2827 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink