GitLab

Shows a toast with instructions to exit VR session right after
session starts.

Also, displays inheadset notifications for previously granted
permissions when entering immersive presentation, and also when
they become in-use.

Bug: 913502, 732449, 934056, 937383
Change-Id: I5d17732da62d07cc7d037160e1914b9fa58f1917
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1527863
Commit-Queue: Suman Kancherla <sumankancherla@chromium.org>
Reviewed-by: Bill Orr <billorr@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646117}