[Worker] Test that no more message events are fired after EventSource.close() is called, even if it means discarding events that were already processed.

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

Starting worker: ../script-tests/eventsource-events-after-close.js
PASS [Worker] es = new EventSource("/eventsource/resources/event-stream.php"); did not throw exception.
PASS [Worker] Got message #1
PASS successfullyParsed is true

TEST COMPLETE