This works for the non-Mac platforms currently. Fix for Mac incoming.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d9068c1138346a06d48de001a1d70184f96f98d5

commit d9068c1138346a06d48de001a1d70184f96f98d5
Author: Justin Donnelly <jdonnelly@chromium.org>
Date: Wed Jul 11 15:05:31 2018

Update features::IsViewsBrowserCocoa() to respect kExperimentalUi.

When we added kExperimentalUi, I added it to
views_mode_controller::IsViewsBrowserCocoa() but I didn't notice
that there was this other implementation.

The omnibox has a feature that uses features::IsViewsBrowserCocoa() and
I'd like it to trigger on kExperimentalUi. Let me know if there's some
reason why we'd expect these to give different answers. There are only a
handful of places that depend on the features:: version:

https://cs.chromium.org/search/?q=features::IsViewsBrowserCocoa

Bug:  862336 
Change-Id: Ieffe5d13bb08c5c36994cef9ccc850ca4552c2b2
Reviewed-on: https://chromium-review.googlesource.com/1132430
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574162}
[modify] https://crrev.com/d9068c1138346a06d48de001a1d70184f96f98d5/chrome/browser/ui/views_mode_controller.cc
[modify] https://crrev.com/d9068c1138346a06d48de001a1d70184f96f98d5/ui/base/ui_base_features.cc