function checkState()
    {
        if (!hasSomethingScheduled()) {
            scheduleShouldFail = false;
            callback();
            return;
        }

        test.addSniffer(throttler, "_processCompletedForTests", checkState);
    }
Waits for current throttler invocations, if any.
@param {!WebInspector.Throttler} throttler
@param {function} callback