ErrorProne: ContextMap

```
48: warning: Inner class is non-static but does not reference enclosing class
    class Connection {
    ^
xxx: warning: Synchronizing on non-final fields is not safe:
  if the field is ever updated, different threads may end up locking on different objects.
        synchronized (mApps) {
                     ^
        synchronized (mConnections) {
                     ^
```

Bug: 236759221
Test: m RUN_ERROR_PRONE=true Bluetooth
Change-Id: I3bc44fc01f5e42f66ddf61e8f5abd5b8cdea5ae7