Merge "MediaSessionRecord: add synchronize control for modification of mControllerCallbackHolders" into main am: 7d782bbb73 am: 0ae8525e0d

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

Change-Id: I9d49a966e66b3ed594d52cd911104f3aaaf3a9f0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>