Fix clipping of squashed sibling layers with border radius masks

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ClipPathClipper.h"
 #include "core/paint/FilterPainter.h"
@@ skipping 956 matching lines @@
     DisplayItem::Type clip_type =
         DisplayItem::PaintPhaseToClipLayerFragmentType(phase);
     LayerClipRecorder::BorderRadiusClippingRule clipping_rule;
     switch (phase) {
       case kPaintPhaseSelfBlockBackgroundOnly:  // Background painting will
                                                 // handle clipping to self.
       case kPaintPhaseSelfOutlineOnly:
       case kPaintPhaseMask:  // Mask painting will handle clipping to self.
         clipping_rule = LayerClipRecorder::kDoNotIncludeSelfForBorderRadius;
         break;
+      case kPaintPhaseClippingMask:
+        if (paint_flags & kPaintLayerPaintingAncestorClippingMaskPhase) {
+          // The ancestor is the thing that needs to clip, so do not include
+          // this layer's clips.
+          clipping_rule = LayerClipRecorder::kDoNotIncludeSelfForBorderRadius;
+          break;
+        }
       default:
         clipping_rule = LayerClipRecorder::kIncludeSelfForBorderRadius;
         break;
     }
 
     // TODO(schenney): Nested border-radius clips are not applied to composited
     // children, probably due to an incorrect clipRoot.
     // https://bugs.chromium.org/p/chromium/issues/detail?id=672561
     clip_recorder.emplace(context, paint_layer_.GetLayoutObject(), clip_type,
                           clip_rect, painting_info.root_layer,
@@ skipping 241 matching lines @@
           context, layout_object, kPaintPhaseClippingMask))
     return;
 
   IntRect snapped_clip_rect = PixelSnappedIntRect(clip_rect.Rect());
   LayoutObjectDrawingRecorder drawing_recorder(
       context, layout_object, kPaintPhaseClippingMask, snapped_clip_rect);
   context.FillRect(snapped_clip_rect, Color::kBlack);
 }
 
 }  // namespace blink