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
public:
  ResolveProxyHelper(AtomBrowserContext* browser_context,
                     const GURL& url,
                     Session::ResolveProxyCallback callback)
      : callback_(callback),
        original_thread_(base::ThreadTaskRunnerHandle::Get()) {
    scoped_refptr<net::URLRequestContextGetter> context_getter =
        browser_context->GetRequestContext();
    context_getter->GetNetworkTaskRunner()->PostTask(
        FROM_HERE,
        base::Bind(&ResolveProxyHelper::ResolveProxy,
                   base::Unretained(this), context_getter, url));
  }
  void OnResolveProxyCompleted(int result) {
    std::string proxy;
    if (result == net::OK)
      proxy = proxy_info_.ToPacString();
    original_thread_->PostTask(FROM_HERE,
                               base::Bind(callback_, proxy));
    delete this;
  }
 private:
  void ResolveProxy(scoped_refptr<net::URLRequestContextGetter> context_getter,