async function getPositionUpdates(workspaceId) {
  const response = workspaceId
    ? await fetch('/api/users/position/query?workspaceId=' + workspaceId)
    : await fetch('/api/users/position/query?');
  const responseJson = await response.json();
  if (response.status === 200) {
    const positionUpdates = responseJson.positionUpdates;
    positionUpdates.forEach((positionUpdate) => {
      positionUpdate.position = Position.fromJson(positionUpdate.position);
    });
    return positionUpdates;
  } else {
    throw 'Failed to get PositionUpdates.';
  }
}
Get the position for the given user. If no user is specified will return
the positions of all users.
@param {string=} workspaceId workspaceId of the user.
@returns {!Promise} Promise object with an array of PositionUpdate objects.
@public