Fix shake-to-reload

sky/framework/debug/shake-to-reload.sky

 <script>
 import '/sky/framework/shell.dart' as shell;
 import 'dart:sky';
 import 'package:sky/services/sensors/sensors.mojom.dart';
 
 // TODO(abarth): We should factor this out into a kinematics library.
 class _ShakeDetector extends SensorListener {
   _ShakeDetector() {
     SensorServiceProxy sensorService = new SensorServiceProxy.unbound();
     shell.requestService(sensorService);
 
-    _stub = new SensorListenerStub.unbound()
-            ..delegate = this;
+    _stub = new SensorListenerStub.unbound()..impl = this;
     sensorService.ptr.addListener(SensorType_ACCELEROMETER, _stub);
-    _stub.listen();
   }
 
   void onAccuracyChanged(int accuracy) {
   }
 
   void onSensorChanged(SensorData data) {
     double value = data.values[0] + data.values[1] + data.values[2];
     if (isShaking && value < 15.0)
       didCompleteShake();
     else if (value > 40.0)
       isShaking = true;
   }
 
   void didCompleteShake() {
     window.location.assign(document.URL);
     _stub.close();
   }
 
   bool isShaking = false;
   SensorListenerStub _stub;
 }
 
 _ShakeDetector _detector;
 
 void _init(_) {
   _detector = new _ShakeDetector();
 }
 </script>