Use control clip rather than overflow clip when present for PaintLayers.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp b/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
index 72d1876fe07a8c2bb93ed83fda2e0e9faffd4880..f86746626204eb7f3b764367d8ffc908a98b0ed4 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
@@ -70,6 +70,14 @@ static void adjustClipRectsForChildren(const LayoutBoxModelObject& layoutObject,
   }
 }
 
+static LayoutRect overflowOrControlClip(const LayoutBox& box,
+                                        const LayoutPoint& location,
+                                        OverlayScrollbarClipBehavior behavior) {
+  if (box.hasControlClip())
+    return box.controlClipRect(location);
+  return box.overflowClipRect(location, behavior);
+}
+
 static void applyClipRects(const ClipRectsContext& context,
                            const LayoutBoxModelObject& layoutObject,
                            LayoutPoint offset,
@@ -87,8 +95,8 @@ static void applyClipRects(const ClipRectsContext& context,
   if (box.hasOverflowClip() ||
       (box.isSVGRoot() && toLayoutSVGRoot(&box)->shouldApplyViewportClip()) ||
       box.styleRef().containsPaint() || box.hasControlClip()) {
-    ClipRect newOverflowClip =
-        box.overflowClipRect(offset, context.overlayScrollbarClipBehavior);
+    ClipRect newOverflowClip = overflowOrControlClip(

[pdr., 2017/01/20 19:17:36]

Can you make the same change in PaintPropertyTreeBuilder::updateOverflowClip?

[chrishtr, 2017/01/20 22:51:10]

Added a TODO. Will do this in another CL because this fixes an M57 regression
and so needs
to be cherrypicked.

+        box, offset, context.overlayScrollbarClipBehavior);
     newOverflowClip.setHasRadius(box.styleRef().hasBorderRadius());
     clipRects.setOverflowClipRect(
         intersection(newOverflowClip, clipRects.overflowClipRect()));
@@ -352,9 +360,10 @@ void PaintLayerClipper::calculateRects(
 
   // Update the clip rects that will be passed to child layers.
   if (shouldClipOverflow(context)) {
-    foregroundRect.intersect(
-        toLayoutBox(layoutObject)
-            .overflowClipRect(offset, context.overlayScrollbarClipBehavior));
+    LayoutRect overflowOrControlClipRect =
+        overflowOrControlClip(toLayoutBox(layoutObject), offset,
+                              context.overlayScrollbarClipBehavior);
+    foregroundRect.intersect(overflowOrControlClipRect);
     if (layoutObject.styleRef().hasBorderRadius())
       foregroundRect.setHasRadius(true);