ServiceWorker

6c1f3fe3 - Change waitUntil behavior; use reference count approach for extension (#1049)

Change waitUntil behavior; use reference count approach for extension (#1049) (1) This removes the extendable event's extensions allowed flag and introduces a reference count based approach instead of the promise-copying-and-checking approach. (2) This extends the opportunities of the lifetime extension by allowing waitUntil() in the task queued by the reaction to the given promise. Fixes #931 #935 #1039 #1050.