Fix a race condition in sensormanager

the per-connection state assumed the main sensorservice
lock was held during access. This is however not true while
pre-processing the events just before sending them to clients.
Therefore, there was a small window during which this state
could be modified while being used.

we now have an internal lock that protects this state.

Change-Id: I594680f20f09d6a4f1f38f093a1d3f650dcef1be
diff --git a/services/sensorservice/SensorService.h b/services/sensorservice/SensorService.h
index b442779..c0922f5 100644
--- a/services/sensorservice/SensorService.h
+++ b/services/sensorservice/SensorService.h
@@ -75,8 +75,9 @@
 
         sp<SensorService> const mService;
         sp<SensorChannel> const mChannel;
+        mutable Mutex mConnectionLock;
 
-        // protected by SensorService::mLock
+        // protected mConnectionLock
         struct SensorInfo {
             SensorInfo() : ns(DEFAULT_EVENTS_PERIOD) { }
             nsecs_t ns;