Merge "[BUG] AudioService: PlaybackActivityMonitor: fix exploding list" am: 3e5cf8398a am: d2648ea1d7

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1421470

Change-Id: I6f2a135237db5c21bf6e54935d4ae7cc379f3d83