private void startCameraSource() throws SecurityException {
    if (mCameraSource != null) {
      mCameraSourcePreview.start(mCameraSource, mGraphicOverlay);
    }
  }
Starts or restarts the camera source, if it exists.

@throws SecurityException if there is no permission to use the camera when this method was
called.
java/com/google/android/apps/authenticator/barcode/BarcodeCaptureActivity.java