ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R action(T argument), { bool runGuarded: true })

Equivalent to:

 ZoneCallback registered = this.registerUnaryCallback(action);
 if (runGuarded) return (arg) => this.runUnaryGuarded(registered, arg);
 return (arg) => thin.runUnary(registered, arg);

Source 

ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R action(T argument),
    {bool runGuarded: true});