add a potential performance TODO in legacy code: T16061: PhabricatorEnv isSelfURI(): add small cache of these self-URIs

Avoid $array[$key]=1 and use $array[$key]=$key as suggested

I suggest testing by setting window width = 1791px (e.g. CTRL+shift+M on Firefox), and then passing to window width = 1792px. So we can see that the content max width at the moment always seems ~ 800px.

Uhm - but looking at your screenshot, at looking here T15920, it seems a regression