commit 59d9ba119448a269289d57e7c3d23a7f04f19248
author David Bokan <bokan@chromium.org> Tue Nov 27 19:17:33 2018
committer Commit Bot <commit-bot@chromium.org> Tue Nov 27 19:17:33 2018
tree b70f6136288de4c3fdfac0d34da697b2deccdace
parent e560cb67cd36c92748011a16444e129e46e77221

[root-scroller] Don't promote when ancestor is scrollable

If we have a candidate implicit root scroller, we should only promote it
if it doesn't have a scrollable ancestor. The reason for this is that we
end scroll chaining at the root scroller. This is necessary as the root
scroller consumes all scroll in the form of overscroll effects. A (user)
scrollable ancestor would be broken in this case, as shown in the
example on the attached bug.

Note: overflow in an ancestor is still allowed, as long as its overflow
style is hidden or visible.

Bug: 837007
Change-Id: Ied7a9f02eab76c4ea59fced94d0804ba47ef4e4a
Reviewed-on: https://chromium-review.googlesource.com/c/1351590
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611245}