Frameworks: Annotate trivial @GuardedBy in media

Add @GuardedBy for simple functions that require a single lock
and are named XYZLocked.

Derived by errorprone.

Bug: 73000847
Test: m
Test: m javac-check-framework RUN_ERROR_PRONE=true
Change-Id: I17e265a771604a06792566c2dd1842f9fe6439e7