Log SignalStrategyType from the client

This change is in preparation for the upcoming signaling changes.
I'd like to start by logging our baseline (XMPP) and then use the
new enum value once FTL is working in Chromium.

Change-Id: I56128ced954a97d18355f67fc2055c08311c1004
Reviewed-on: https://chromium-review.googlesource.com/c/1413066
Reviewed-by: Yuwei Huang <yuweih@chromium.org>
Commit-Queue: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623060}
8 files changed