[remoting][mobile] Send session-terminate when user disconnects

Mobile apps were not sending session-terminate to the host when the
user taps the disconnect button. This delays resource cleanup on the
host side and skews the telemetry data sent from the host (although
we never look at them). Note that the client does send a close event
to telemetry.

This CL makes sure mobile clients send a session-terminate message to
the host for user initiated disconnection. It has a side effect such
that user will see a toast that says "Your Chrome Remote Desktop
session has ended." when the user taps the disconnect button, but that
seems fine to me.

Bug: 970054
Change-Id: Idf48c33e0e3d06b3079cd7f50b603b897f6abd79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674703
Commit-Queue: Joe Downing <joedow@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672279}
10 files changed