not just alert but also prompt(), confirm(), etc. And from what I can tell there's not even an option to turn them back on, like some other sandbox rules that are available from iframes (not 100% certain about this but that was my takeaway skimming the relevant bug report on monorail)
This is Google trying to eliminate part of a web standard because their WebKit implementation is bad and those things block the event loop and cause all kinds of headaches.<p>I would prefer an os-native alert() over some monstrosity of a jQuery UI message box any day...