Merge from http://go/wvgerrit/47640
Test: unit/integration tests
Bug: b/62058202
The usage table keeps track of license duration by using the current
system time. However, if a user were to rollback the time, they can
effectively continue offline playback indefinitely. This changes the way
we compute time by computing offsets by which the user rollbacked the
time and adding it to the current time. This change also includes a test
to verify protection against rollback for usage entries that is only run
when the user is root.
Change-Id: I97c430e1443747b0f9759ae5390b8f5d06bdebf1
73c3007c24