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
return browser_context_->GetUserAgent();
}
v8::Local<v8::Value> Session::Cookies(v8::Isolate* isolate) {
  if (cookies_.IsEmpty()) {
    auto handle = atom::api::Cookies::Create(isolate, browser_context());
    cookies_.Reset(isolate, handle.ToV8());
  }
  return v8::Local<v8::Value>::New(isolate, cookies_);
}
v8::Local<v8::Value> Session::Protocol(v8::Isolate* isolate) {
  if (protocol_.IsEmpty()) {
    auto handle = atom::api::Protocol::Create(isolate, browser_context());
    protocol_.Reset(isolate, handle.ToV8());
  }
  return v8::Local<v8::Value>::New(isolate, protocol_);
}
v8::Local<v8::Value> Session::WebRequest(v8::Isolate* isolate) {
  if (web_request_.IsEmpty()) {
    auto handle = atom::api::WebRequest::Create(isolate, browser_context());
    web_request_.Reset(isolate, handle.ToV8());
  }
  return v8::Local<v8::Value>::New(isolate, web_request_);
}
mate::Handle<Session> Session::CreateFrom(