MediaSessionManager: Use Executor instead of Handler

Bug: 138648566
Test: Build
Change-Id: I89a612cb1408dfb2cc4f624c7e0f8c8a55e0a732
Merged-In: I89a612cb1408dfb2cc4f624c7e0f8c8a55e0a732
(cherry picked from commit 95c783e2d2b4fe061dc6b128301174f2115ec1d0)
2 files changed