GitLab

Adds metrics around advertisement registration/unregistration,
scanning, creating a GATT connection, and the StartNotify operation.

These metrics are being created in addition to existing similar
Bluetooth metrics in order to gauge Tether's stability as a client
versus Bluetooth as a whole.

Bug: 
Change-Id: Idf719394e4193591230cc765d48a8ceb0a0f4b88
Reviewed-on: https://chromium-review.googlesource.com/701373Reviewed-by: Tim Song <tengs@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Jeremy Klein <jlklein@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506784}