Account for overlay scrollbars when computing scrollbar width/height.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 5e1cd751f37909144240a811091817055e5d786a..c8523dcf456d0ae3bdc2fdc9567c761dfc4300f1 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1284,10 +1284,12 @@ int PaintLayerScrollableArea::verticalScrollbarWidth(
     OverlayScrollbarClipBehavior overlayScrollbarClipBehavior) const {
   if (!hasVerticalScrollbar())
     return 0;
-  if (verticalScrollbar()->isOverlayScrollbar() &&
+  if ((verticalScrollbar()->isOverlayScrollbar() ||
+       box().style()->overflowY() == EOverflow::kOverlay) &&
       (overlayScrollbarClipBehavior == IgnoreOverlayScrollbarSize ||
-       !verticalScrollbar()->shouldParticipateInHitTesting()))
+       !verticalScrollbar()->shouldParticipateInHitTesting())) {
     return 0;
+  }
   return verticalScrollbar()->scrollbarThickness();
 }
 
@@ -1295,10 +1297,12 @@ int PaintLayerScrollableArea::horizontalScrollbarHeight(
     OverlayScrollbarClipBehavior overlayScrollbarClipBehavior) const {
   if (!hasHorizontalScrollbar())
     return 0;
-  if (horizontalScrollbar()->isOverlayScrollbar() &&
+  if ((horizontalScrollbar()->isOverlayScrollbar() ||
+       box().style()->overflowX() == EOverflow::kOverlay) &&
       (overlayScrollbarClipBehavior == IgnoreOverlayScrollbarSize ||
-       !horizontalScrollbar()->shouldParticipateInHitTesting()))
+       !horizontalScrollbar()->shouldParticipateInHitTesting())) {
     return 0;
+  }
   return horizontalScrollbar()->scrollbarThickness();
 }