Trace currently resumed app

Since we now have the ability to multi-hour systraces from
devices used daily, it's useful to do additional segmentation
and understanding what part of an app's runtime is due to it
being in foreground vs background.

Test: go/wm-smoke
Test: Take trace, check whether currently resumed app is being
traced.

Bug: 69862220
Change-Id: Idaf9af4c366dfedb29d07b75f7eaf17d9a2165a0