Bug 1062805 - Used the shared JSON file load helper in the ringtones app R=Goutam

I don't really know the code, I think you need to return the promise here instead of the new promise above.

Something like (untested code):
```javascript
if (toneType in toneDefsCache) {
  return Promise.resolve(toneDefsCache[toneType]);
}

return LazyLoader.getJSON....then( ... );
```