Fix nested border radius with composited child.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h

 /*
  * Copyright (C) 2009, 2010, 2011 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 470 matching lines @@
   // contains this squashed layer's clipping ancestor.  The clip rect is
   // returned in the coordinate space of the given squashed layer.  If there is
   // no such containing layer, returns the infinite rect.
   // FIXME: unify this code with the code that sets up m_ancestorClippingLayer.
   // They are doing very similar things.
   static IntRect LocalClipRectForSquashedLayer(
       const PaintLayer& reference_layer,
       const GraphicsLayerPaintInfo&,
       const Vector<GraphicsLayerPaintInfo>& layers);
 
-  // Conservatively check that a border-radius clip does not clip a child.
+  // Conservatively check that a sequence of border-radius clips do not clip
+  // this layer.
   // This is a fast approximate test. Depending on the shape of the child and
-  // the size of the border radius, this method may return false when in fact
+  // the size of the clips, this method may return false when in fact
   // the child is not clipped. We accept the approximation because most border
   // radii are small and the outcome is used to reduce the number of layers,
   // not influence correctness.
-  bool AncestorRoundedCornersWontClip(
-      const LayoutBoxModelObject& child,
-      const LayoutBoxModelObject& clipping_ancestor);
+  bool AncestorRoundedCornersWontClip(const PaintLayer*);

[chrishtr, 2017/06/12 19:58:46]

Name this arg compositing_ancestor and add documentation for it.

[Stephen Chennney, 2017/06/12 20:41:53]

Done.

 
   // Return true in |owningLayerIsClipped| iff |m_owningLayer|'s compositing
   // ancestor is not a descendant (inclusive) of the clipping container for
   // |m_owningLayer|. Return true in |owningLayerIsMasked| iff
   // |owningLayerIsClipped| is true and |m_owningLayer|'s compositing ancestor
   // is not a descendant (inclusive) of a container that applies a mask for
   // |m_owningLayer|.
   void OwningLayerClippedOrMaskedByLayerNotAboveCompositedAncestor(
       const PaintLayer* scroll_parent,
       bool& owning_layer_is_clipped,
@@ skipping 197 matching lines @@
   unsigned background_paints_onto_graphics_layer_ : 1;
 
   bool draws_background_onto_content_layer_;
 
   friend class CompositedLayerMappingTest;
 };
 
 }  // namespace blink
 
 #endif  // CompositedLayerMapping_h