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 f9320de2ecbc1121d69e6f67d14d7989fe630dc2..7537e0d0548627b017f8c1871bd45686ecd8df68 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -961,7 +961,9 @@ void PaintLayerPainter::PaintFragmentWithPhase(
       case kPaintPhaseSelfBlockBackgroundOnly:  // Background painting will
                                                 // handle clipping to self.
       case kPaintPhaseSelfOutlineOnly:
-      case kPaintPhaseMask:  // Mask painting will handle clipping to self.
+      case kPaintPhaseMask:
+      case kPaintPhaseClippingMask:

[chrishtr, 2017/04/17 17:25:00]

Your fix is generally correct, just a small error. kPaintPhaseClippingMask can
be true
for more than just ancestor mask clips. If you use this code instead, it should
work:

case kPaintPhaseClippingMask:
        if (paint_flags & kPaintLayerPaintingAncestorClippingMaskPhase) {
          clipping_rule = LayerClipRecorder::kDoNotIncludeSelfForBorderRadius;
          break;
        }

+        // Mask painting will handle clipping to self.
         clipping_rule = LayerClipRecorder::kDoNotIncludeSelfForBorderRadius;
         break;
       default: