[ServiceWorker] Promises inside Service workers don't throw errors (#600)

Also, reported this bug here, https://code.google.com/p/chromium/issues/detail?id=448281 

```javascript
this.addEventListener('install', function(event) {
 event.waitUntil(
  caches
   .open('demo')
   .then(function() {
    throw new Error('Blah Blah');
   })
 );
});
```

doesn't throw the error. It is being caught somewhere.

Also, whenever this error happens, the service worker is registered and immediately unregistered. And when refreshing the page, a new worker with an incremented version ID is registered and the same happens because of the error, and this error is never thrown.

![screenshot 2015-01-13 11 28 55](https://cloud.githubusercontent.com/assets/294474/5716701/8839d19a-9b19-11e4-8628-f1705c1a6fa3.png)
![screenshot 2015-01-13 11 29 15](https://cloud.githubusercontent.com/assets/294474/5716700/8837498e-9b19-11e4-92e0-7cfaa1e28c8e.png)



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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/600