anchor.diff:    return new AndroidBackButtonMemoryTest(
       '${flutterDirectory.path}/examples/flutter_gallery',
       'io.flutter.examples.gallery',
  +    'io.flutter.examples.gallery.MainActivity',
     );
   }
   
  
positive.code: class AndroidBackButtonMemoryTest {
    final String testDirectory;
    final String packageName;
  
    AndroidBackButtonMemoryTest(this.testDirectory, this.packageName);
  
    Future<TaskResult> call() {
      return inDirectory(testDirectory, () async {
  
negative.code:       for (int i = 0; i < 10; i++) {
          await device.shellExec('input', <String>['keyevent', 'KEYCODE_BACK']);
          await new Future<Null>.delayed(const Duration(milliseconds: 1000));
          final String output = await device.shellEval('am', <String>['start', '-n', '$packageName/$activityName']);
          print(output);
          if (output.contains('Error'))
            return new TaskResult.failure('unable to launch activity');
  