Add Google Analytics support to tr.b.Timing.
Add Google Analytics support to tr.b.Timing.

This also refactors the Mark object to a class so that callers can access
everything about it including its duration.

This also adds tr.b.Timing.instant() to allow callers to log non-latency numeric
parameters (e.g. histogram count, trace event count, etc.) to both the devtools
trace timeline and Google Analytics.

See usage in https://codereview.chromium.org/2847893004

BUG=catapult:#3416

Review-Url: https://codereview.chromium.org/2870663002

benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult-csm