Use TotalTime instead of ThisTime as app launch latency metric

Use TotalTime instead of ThisTime as app launch latency metric

Use TotalTime instead of ThisTime (both reported by am) as our
activity launch latency metric. TotalTime is more representative
of user perceived latency. Also add back YouTube to the list of
apps we launch test by default.

Test: Time app launches manually for the various apps, and check
that TotalTime better represents the launch latency.

Change-Id: I127a22ae409ee0141d847e711e09f7873dbb420f
Signed-off-by: Mohan Srinivasan <srmohan@google.com>