Go to the linked url, start the debugger. Set a breakpoint on the render function in rayjs.html click the render link, the dbeugger should hit your break point. Now hit the render link again, and the renderer will start, trigger the slow script dialog, *and* continue working without hitting any break points that may otherwise have been present (if you allow it to continue after the slow script dialog).
<rdar://problem/6126886>
Created attachment 22817 [details] Proposed patch (ignoring whitespace changes)
Created attachment 22818 [details] Proposed patch (full patch)
Comment on attachment 22817 [details] Proposed patch (ignoring whitespace changes) r=me Nice test case!
Landed in r35783.