Fix clipping of squashed sibling layers with border radius masks

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

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index df10d3cbeb2c046be32caad70f366c872530367f..039a63448a6a8a8ad736045e68bf9cf0ce584d04 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -974,6 +974,13 @@ void PaintLayerPainter::PaintFragmentWithPhase(
       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;