The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3973180d868cd479dd049f16096800f7a5678f1d

commit 3973180d868cd479dd049f16096800f7a5678f1d
Author: Ehsan Karamad <ekaramad@chromium.org>
Date: Wed Oct 31 22:18:31 2018

No vertical bars if 'vertical-policy' disabled

When 'vertical-scroll' policy is disabled in a document, the contents
cannot be scrolled (will not be user-input scrollable and targeted
for gesture scroll). However, currently disabling 'vertical-scroll'
still leaves the vertical scrollbars behind; the bars position cannot
be changed however.

This CL fixes the issue by hiding the vertical scrollbars for
scrollable elements inside documents where the policy is enforced
(i.e., disabled).

Bug:  898151 
Change-Id: If01925e27184a7370d5b12583dc73bc946f2c6e2
Reviewed-on: https://chromium-review.googlesource.com/c/1305878
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604420}
[add] https://crrev.com/3973180d868cd479dd049f16096800f7a5678f1d/third_party/WebKit/LayoutTests/external/wpt/feature-policy/experimental-features/resources/vertical-scroll-scrollbar-ref.html
[add] https://crrev.com/3973180d868cd479dd049f16096800f7a5678f1d/third_party/WebKit/LayoutTests/external/wpt/feature-policy/experimental-features/vertical-scroll-disabled-scrollbar-tentative.html
[modify] https://crrev.com/3973180d868cd479dd049f16096800f7a5678f1d/third_party/blink/renderer/core/paint/paint_layer_scrollable_area.cc