Merge "MidiService: synchronize mDeviceConnections" into sc-dev am: e65c02b2 am: 918c8a99 am: f03b67be

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

Change-Id: I83ecdcced4afb7705fc0498fc4e68afbc55dbb3b