GitLab

https://chromium-review.googlesource.com/c/542962/ was reverted due to
a bug, however, part of the changes are still useful, so restore them
in this CL. And specifically, this CL refactors CRWWebController and
web view creation utils to use UserAgentType.

Bug: 
Change-Id: Iafaca12bd30d1b84b315295ee090e7ee68161bfe
Reviewed-on: https://chromium-review.googlesource.com/545112
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481922}