Code review comment for lp:~unity-team/unity/3v1n0-quick-alt+tab-fixes

Probably it is caused by the fact that now we use a very small delay for the Alt+Tab.
A workaround could be to use another time reference to consider an Alt+Tab quick, more than the only window visibility.

I mean, even if the window is shown for 100ms or less, the Alt+Tab is surely a quick one (as there's no time to look to the content of the window).