[ServiceWorker] Cancelling HTTP fetch (#592)

When the user clicks the stop button while the page is loading a large file (example: a movie file) via the ServiceWorker, the ServiceWoer should stop the HTTP fetching to reduce the resource usage.

```JavaScript
self.addEventListener('fetch', function(event) {
  event.respondWith(fetch(event.request));
});
```


Is this behavior specified in the Fetch spec or the ServiceWorker spec?

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/592