function HttpPoller(target, timeout, callback) {
  HttpPoller.super_.call(this, target, timeout, callback);
}
HTTP Poller, to check web pages

@param {Mixed} Poller Target (e.g. URL)
@param {Number} Poller timeout in milliseconds. Without response before this duration, the poller stops and executes the error callback.
@param {Function} Error/success callback
@api   public