Implement IndexedDB's oncomplete and ontimeout.
Created attachment 69671 [details]
We should also update the rest of the layout tests as they all use transactions now.
> window.completeEventFired = false;
Here and below: maybe assert that the timer is not active? If it is, something's wrong but we won't see this as the timer will just be postponed.
Created attachment 69687 [details]
Was landed in 69052