Only honor the scrollbar mode at the minimum zoom

level. This reduced the impact of https://android-git.corp.google.com/g/#change,48683.
In GB, we need to revisit this issue.

Wit this CL, http://b/issue?id=2512549 is still fine.

Fix http://b/issue?id=2619398
It should fix http://b/issue?id=2619415 when it is not in zoom out case.
It doesn't fix http://b/issue?id=2620979 as the site
is a mobile site. We have conflict with the requirement
from http://b/issue?id=2512549