async function sendPositionUpdate(positionUpdate) {
  const response = await fetch('/api/users/position/update', {
    method: 'PUT',
    body: JSON.stringify({positionUpdate}),
  });
  if (response.status === 200) {
    return;
  } else {
    throw 'Failed to update position.';
  }
}
Update the position of a user in the database.
@param {!PositionUpdate} positionUpdate The PositionUpdate with the new
position for a given user.
@returns {!Promise} Promise object representing the success of the update.
@public