Revert "[RootScroller] Allow main document horizontal overflow"

This reverts commit ace3f1f79bf62fe4f30ae014d8d19caecc94e997.

Reason for revert: Checking to see if this caused flaky scrolling failures on Mac 10.13 ( )

Original change's description:
> [RootScroller] Allow main document horizontal overflow
> When implicitly promoting an element to be the root scroller, we first
> check if the main document has any overflow. If it does, we err on the
> side of not promoting since it is likely the main document's content is
> important and meant to be scrollable.
> This heuristic turns out to be too restrictive. For example, this makes
> it hard to build a root scrolling carousel. This CL loosens the
> restriction to allow horizontal overflow.
> Bug: 838683
> Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
> Change-Id: I6007f6faa8e2006799a9dca6240b68ff0de7f09a
> Reviewed-on:
> Commit-Queue: David Bokan <>
> Reviewed-by: Dave Tapuska <>
> Cr-Commit-Position: refs/heads/master@{#581408},

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 838683
Change-Id: I14e6a0158bb8b06f2344c3b30b38b86c6eabd583
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Reviewed-by: Peter Kasting <>
Commit-Queue: Peter Kasting <>
Cr-Commit-Position: refs/heads/master@{#582439}
3 files changed