GitLab

Moving Trusted Web Activities over to CustomTabActivity gets us
PostMessage for free. Unfortunately we're not ready to launch that,
so disable it for the time being.

Bug: 871266
Change-Id: Iaef2c08aea87be888cd98b102aeb4a87e888fd04
Reviewed-on: https://chromium-review.googlesource.com/1181139Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Peter Conn <peconn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584473}