Fix nested border radius with composited child.

third_party/WebKit/Source/core/paint/PaintLayerPaintingInfo.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 78 matching lines @@
       : root_layer(in_root_layer),
         paint_dirty_rect(in_dirty_rect),
         sub_pixel_accumulation(in_sub_pixel_accumulation),
         clip_to_dirty_rect(true),
         ancestor_has_clip_path_clipping(false),
         global_paint_flags_(global_paint_flags) {}
 
   GlobalPaintFlags GetGlobalPaintFlags() const { return global_paint_flags_; }
 
   // TODO(jchaffraix): We should encapsulate all these fields.
-  PaintLayer* root_layer;
+  const PaintLayer* root_layer;
   LayoutRect paint_dirty_rect;  // relative to rootLayer;
   LayoutSize sub_pixel_accumulation;
   IntSize scroll_offset_accumulation;
   bool clip_to_dirty_rect;
   bool ancestor_has_clip_path_clipping;
 
  private:
   const GlobalPaintFlags global_paint_flags_;
 };
 
 }  // namespace blink
 
 #endif  // PaintLayerPaintingInfo_h