Add new ConnectionEvent API (hide) to send a notification to Telecom

Connection event used to inform Telecom that it should play or stop
the on hold tone. This is used to play or stop a tone when the peer
puts the current call on hold.

BUG=25357778
Change-Id: I2669f8f5062449784a712b9dd28e576326fcc679

telecomm/java/android/telecom/ConnectionService.java

@@ -613,6 +613,14 @@ public abstract class ConnectionService extends Service {
                 mAdapter.setExtras(id, extras);
             }
         }
+
+        @Override
+        public void onConnectionEvent(Connection connection, String event) {
+            String id = mIdByConnection.get(connection);
+            if (id != null) {
+                mAdapter.onConnectionEvent(id, event);
+            }
+        }
     };
 
     /** {@inheritDoc} */