@Override
            public BarcodeDetector call() {
              return new BarcodeDetector.Builder(getApplicationContext())
                  .setBarcodeFormats(Barcode.QR_CODE)
                  .build();
            }
Building the barcode detector is an expensive operation (~1000ms), so we are building it in
another thread and cached it. This barcode detector only detects QR code format.
java/com/google/android/apps/authenticator/AuthenticatorApplication.java