Test WorkerContext.close functionality. Should print a series of PASS messages, followed with DONE.

PASS: typeof close: function
PASS: received message before close
PASS: Received message posted right after close() was invoked: Should be delivered
PASS: no messages arrive to worker after JS fragment with close() exits
PASS: Error arrived after close: ReferenceError: Can't find variable: nonExistentFunction
PASS: close() did not dispatch pending events
PASS: Received message after worker closed: Should be delivered
DONE