GitLab

This adds message handlers for a few things that were added
semi-recently to the non-iOS version.
Also includes a few tiny cleanups to the non-iOS message handler.

Bug: 898439
Change-Id: I38dc6d643c1b9ad6fd3608d8a4ed799385d7d946
Reviewed-on: https://chromium-review.googlesource.com/c/1315209
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605308}