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

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 52 matching lines @@
     clipRects.setPosClipRect(clipRects.fixedClipRect());
     clipRects.setOverflowClipRect(clipRects.fixedClipRect());
     clipRects.setFixed(true);
   } else if (position == RelativePosition) {
     clipRects.setPosClipRect(clipRects.overflowClipRect());
   } else if (position == AbsolutePosition) {
     clipRects.setOverflowClipRect(clipRects.posClipRect());
   }
 }
 
+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,
                            ClipRects& clipRects) {
   DCHECK(layoutObject.isBox());
   const LayoutBox& box = *toLayoutBox(&layoutObject);
 
   DCHECK(box.hasClipRelatedProperty() || box.hasControlClip() ||
          (box.isSVGRoot() && toLayoutSVGRoot(&box)->shouldApplyViewportClip()));
   LayoutView* view = box.view();
   DCHECK(view);
   if (clipRects.fixed() && context.rootLayer->layoutObject() == view)
     offset -= LayoutSize(view->frameView()->getScrollOffset());
 
   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()));
     if (box.isPositioned())
       clipRects.setPosClipRect(
           intersection(newOverflowClip, clipRects.posClipRect()));
     if (box.isLayoutView() || box.hasTransformRelatedProperty())
       clipRects.setFixedClipRect(
           intersection(newOverflowClip, clipRects.fixedClipRect()));
     if (box.styleRef().containsPaint()) {
@@ skipping 243 matching lines @@
 
   LayoutPoint offset;
   if (offsetFromRoot)
     offset = *offsetFromRoot;
   else
     m_layer.convertToLayerCoords(context.rootLayer, offset);
   layerBounds = LayoutRect(offset, LayoutSize(m_layer.size()));
 
   // 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);
 
     // FIXME: Does not do the right thing with columns yet, since we don't yet
     // factor in the individual column boxes as overflow.
 
     // The LayoutView is special since its overflow clipping rect may be larger
     // than its box rect (crbug.com/492871).
     LayoutRect layerBoundsWithVisualOverflow =
         layoutObject.isLayoutView()
@@ skipping 209 matching lines @@
     const LayoutSize& subpixelAccumulation) const {
   DCHECK(!m_geometryMapper);
   ClipRectsContext context(rootLayer, PaintingClipRects,
                            IgnoreOverlayScrollbarSize, subpixelAccumulation);
   if (respectOverflowClip == IgnoreOverflowClip)
     context.setIgnoreOverflowClip();
   return getClipRects(context);
 }
 
 }  // namespace blink