If you hold down the left arrow key in Google Maps street view to take a look around you, sometimes the runaway JavaScript alert comes up. To reproduce, open the URL, click in the street view and press and hold down the left arrow key. This is not 100% reproducible.
Created attachment 15014 [details] Backtrace when the timer fired
Created attachment 15015 [details] Another backtrace from when shouldInterruptScript was called
Committed revision 23526.