Expand nuplayer mutex for mediametrics management

refactor some mutex for how nuplayer sets up mediametrics data.
expanded locking to eliminate a couple race conditions.

Bug: 151644303
Bug: 151643722
Test: poc attached to bugs
Merged-In: I75f29a6254c5eab5d4f524ee7a7ef59f93a0b405
Merged-In: Ia2e68ef616e249a6e8746b9068f22bd208a0ffc8
Merged-In: I1e9bbcd67a1510f70fad66e8ef77f529008e248a
Merged-In: I9c473e47e7eb8dce24399bcb24f82a3d2d583983
Change-Id: If9aeff27e14370bd8104acab1d2b0058d82874fd