Fix border radius on composited children.

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
@@ skipping 2259 matching lines @@
     return false;
 
   // If the box has clip or mask, we need issue paint invalidation to cover
   // the changed part of children when the box got resized. In SPv2 this is
   // handled by detecting paint property changes.
   if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
     if (hasClipRelatedProperty() || hasControlClip() || hasMask())
       return false;
   }
 
+  // If the box paints into its own backing, we can assume that it's painting
+  // may have some effect. For example, honoring the border-radius clip on
+  // a composited child paints into a mask for an otherwise non-painting
+  // element, because children of that element will require the mask.
+  if (hasLayer() && layer()->compositingState() == PaintsIntoOwnBacking)
+    return false;
+
   return true;
 }
 
 LayoutRect LayoutBox::localVisualRect() const {
   if (style()->visibility() != EVisibility::Visible)
     return LayoutRect();
 
   if (hasMask() && !RuntimeEnabledFeatures::slimmingPaintV2Enabled())
     return LayoutRect(layer()->boxForFilterOrMask());
   return selfVisualOverflowRect();
@@ skipping 3399 matching lines @@
     block->adjustChildDebugRect(rect);
 
   return rect;
 }
 
 bool LayoutBox::shouldClipOverflow() const {
   return hasOverflowClip() || styleRef().containsPaint() || hasControlClip();
 }
 
 }  // namespace blink