| Tests the returnValue attribute of the BeforeUnloadEvent. | |
| On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". | |
| PASS testEvent.__proto__ is iframe.contentWindow.BeforeUnloadEvent.prototype | |
| PASS testEvent.returnValue is "" | |
| PASS testEvent.returnValue is "This is beforeunload from the top level frame." | |
| PASS successfullyParsed is true | |
| TEST COMPLETE | |