[TIMOB-3025] Android: Facebook.logout called from activity destroy event doesn't (always) succeed in clearing saved session info

Some app developers want to clear the saved Facebook session information when a user backs out of an app, so that the session info doesn't automatically get remembered the next time the app is started. I want to recommend to them that they should use the destroy event of the root activity, such as in this example app.js:

Titanium.UI.setBackgroundColor('#000');
Ti.Facebook.appid = "PUT A FACEBOOK APP ID HERE";
var win = Titanium.UI.createWindow({  
    title:'Test',
    backgroundColor:'#fff',
    exitOnClose: true
});

Ti.Android.currentActivity.addEventListener('destroy',function(){
    Ti.API.info('Root activity destroying');
    Ti.Facebook.logout();
});
win.add( Ti.Facebook.createLoginButton({style: 'wide'}) );
win.open();

Run that example and login to Facebook. Then completely back out of the application. Then go back in to the application -- unfortunately you'll probably see the facebook button still says "logout", so it thinks it is logged in even though we called logout() when the user backed out of the app, which is when destroy occurs (you can see that logout() really does get called if you watch logcat.

So what has happened is that the user really is logged out of that Facebook session (the OAuth 2.0 token is no longer valid), but Titanium doesn't know about it, so the login button is screwed up and showing "Logout" instead of "Connect with Facebook".

I think what's happening here is that the relevant Titanium code to clear the saved session info (saved as a private entry in the Android Shared Preferences store) does not run until an Asynchronous call to Facebook's logout API has returned. By the time that Async call is finished, there are no listeners available any more (the user has backed out of the app, the root activity has been destroyed, etc.)

What we need to do is destroy the session info right when Ti.Facebook.logout() is called, rather than wait for a return from FB's logout API call. After all, if an app developer has called .logout(), he wants that session destroyed, so why wait? This way the destruction of the session occurs synchronously within the destroy thread.