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 a9aaa381dcaa511e54ed9ac049395b7972004827..df6ec5704fbe81fcb5c7b0760fddb9bd21ad89b1 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -953,6 +953,13 @@ void PaintLayerPainter::paintFragmentWithPhase(
       case PaintPhaseMask:  // Mask painting will handle clipping to self.
         clippingRule = LayerClipRecorder::DoNotIncludeSelfForBorderRadius;
         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:
         clippingRule = LayerClipRecorder::IncludeSelfForBorderRadius;
         break;