Report all fires of window.onerror.

Additionally, mark the test as having results so that it
won't be ran again. The reported URL is simplified if possible.

## TODO
 - [ ] Expose these fires as test results and fire `results` event with simulated failures.
 - [ ] Investigate why `test.location` does not always work.
 - [ ] Only abort the current test on `scriptError` if the tests can no longer run, otherwise also run test results and include the uncaught error in the results object.