mocking location.prototype in javascript for jasmine unit testing

The following code is working for mocking the userAgent string for unit testing in Jasmine.

it('check browser name and version',function(){

    var __originalNavigator = navigator;
    var navigator = new Object();
    navigator.__proto__ = __originalNavigator;
    navigator.__defineGetter__('userAgent', function () { return 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20130401 Firefox/31.0'; });

    var isFirefox = browserCheck.isFirefox();
    expect(isFirefox).toBe(true);

});

Where as the similar following code is not working.

it('check browser security protocol',function(){
        var __originalPrototype = window.location;
        window.location = new Object();
        window.location.__proto__ = __originalPrototype;
        window.location.__defineGetter__('protocol', function () {     return 'https:'; });

        var isSecure = BrowserCheck.checkSecurity();
                expect(isFirefox).toBe(true);
});

My question is mainly about mocking the window.location.