code: public void rotateToFaceCamera(final GVRTransform transform) {
          //see http://stackoverflow.com/questions/5782658/extracting-yaw-from-a-quaternion
          final GVRTransform t = getMainCameraRig().getHeadTransform();
          final Quaternionf q = new Quaternionf(0, t.getRotationY(), 0, t.getRotationW()).normalize();
  
          transform.rotateWithPivot(q.w, q.x, q.y, q.z, 0, 0, 0);
      }
docs: Apply the necessary rotation to the transform so that it is in front of
  the camera.
  
  @param transform The transform to modify.