Do you remember why this one is needed? It causes cookies to be set even if they might be disabled later via Tracker.disableCookies. Can we remove it from the constructor?

If this line is commented then following tests fail:

These tests were written to document the existing behaviour. I'm not 100% sure that these tests are correct but I think they are mostly correct... Let me know if you want more info

setVisitorIdCookie() is only executed if Piwik.getTracker(url, siteId) is actually called this way and provided with a siteId. In all other cases (meaning when the default async tracker is used via _paq) this method will not have an effect since the method setVisitorIdCookie() will only do something if configTrackerSiteId is set.

The tests succeed when updating the test to eg from

var delayedTracker = Piwik.getTracker();

to

var delayedTracker = Piwik.getTracker();
delayedTracker.setSiteId(1);

which would be better. I think it is rather an accident that this test works because the tests are not atomic and do not reset everything in each test suite. In reality one would have to set at least a siteId making everything work again. This would also give developers a chance to do the following if they want:

var delayedTracker = Piwik.getTracker();
delayedTracker.disableCookies();
delayedTracker.setSiteId(1);

We should maybe remove the parameter siteId from Piwik.getTracker() at some point and for now just recommend to not use it if they want to use disableCookies