Merge "MediaSessionRecord: add synchronize control for modification of mControllerCallbackHolders" into main am: 7d782bbb73

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/3013135

Change-Id: Ib79715f3d0e460823b74bf29b2d3ed5ace33faf9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>