Might be nice to throw the error again if it's not a `QUOTA_EXCEEDED_ERR`?

```js
try {
  localStorage.setItem('backboneCache', JSON.stringify(Backbone.fetchCache._cache));
} catch (err) {
  if (err.name === 'QUOTA_EXCEEDED_ERR') {
    this.deleteCacheWithPriority();
  } else {
    throw(err);
  }
}
```