WebFullScreenController and WKFullScreenWindowController both add a method named convertRectToScreen: on to NSWindow via a category when building for 10.6 and earlier. This causes problems when building for 10.6 against a newer SDK as NSWindow already has a method of that name. It's also unhygienic as it could interfere with a client application that provides methods of the same name.
Created attachment 151794 [details]
Landed in r122403.