ServiceWorker

8538a55d - Make ServiceWorker/ExtendableMessageEvent's ports non-nullable

Make ServiceWorker/ExtendableMessageEvent's ports non-nullable Update the ServiceWorker/ExtendableMessageEvent IDL conforming to the latest HTML changes: - Make ports attribute non-nullable - Change the type of the origin attribute from DOMString to USVString - Assign default values to the corresponding Init dictionaries Fixes #989