Merge "MediaSyncEvent: Fix thread safety" am: d84c55fba0 am: 3c99f759e4 am: 41e1bb49ee

Original change: https://android-review.googlesource.com/c/platform/frameworks/av/+/2599069

Change-Id: I3924390245d2d387f17a0c7b6815e59607117acc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>