RC: Add reason arg to LifecycleUnitObserver::OnLifecycleUnitStateChanged().

The state change reason should be logged with every discard metric,
to allow proper interpretation.

Adding the state change reason to the observer interface is the first
step towards adding it to every metric.

Bug: 775644
Change-Id: I671ca55494a50bb99e89e8bdd1ec0b18dbe281cb
Reviewed-on: https://chromium-review.googlesource.com/1136949
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575512}
11 files changed