Merge "MidiService: synchronize mDeviceConnections" into sc-dev am: e65c02b2 am: 947827c6 am: 9b58e266

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15317991

Change-Id: I11cf1d96f5a2f8a2506144eba38511e7278f8f3f