Docs:
https://github.com/electron/electron/blob/master/docs/api/session.md#sesclearstoragedataoptions-callback

I was running into a strange error when calling the `clearStorageData` method. It was saying it was unable to process the argument at index 1, which I was not passing. After some research I found that the callback is currently required, but in my case I did not care to provide one. To fix it, I supplied an empty function. Here is my code:

```
Electron.remote.getCurrentWebContents().session.clearStorageData(
    {
        storages: [
            'appcache',
            'cookies',
            'filesystem',
            'indexdb',
            'localstorage',
            'shadercache',
            'websql',
            'serviceworkers',
        ],
        quotas: [
            'temporary',
            'persistent',
            'syncable',
        ],
    },
    function() {} // <--- I shouldn't have to do this
);
```
- Electron version: 1.2.7
- Operating system: macOS

atom/browser/api/atom_api_session.cc
BrowserThread::PostTask(
      BrowserThread::UI, FROM_HERE, base::Bind(callback, result...));
}
void OnGetBackend(disk_cache::Backend** backend_ptr,
                  Session::CacheAction action,
                  const net::CompletionCallback& callback,
                  int result) {
  if (result != net::OK) {
    RunCallbackInUI(callback, result);
  } else if (backend_ptr && *backend_ptr) {
    if (action == Session::CacheAction::CLEAR) {
      (*backend_ptr)->DoomAllEntries(base::Bind(&RunCallbackInUI<int>,
                                                callback));
    } else if (action == Session::CacheAction::STATS) {
      base::StringPairs stats;
      (*backend_ptr)->GetStats(&stats);
      for (const auto& stat : stats) {
        if (stat.first == "Current size") {
          int current_size;
          base::StringToInt(stat.second, &current_size);
          RunCallbackInUI(callback, current_size);
          break;
        }
      }
    }
  } else {
    RunCallbackInUI<int>(callback, net::ERR_FAILED);
  }
}
void DoCacheActionInIO(