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
v8::Local<v8::Value> val,
                     ClearStorageDataOptions* out) {
    mate::Dictionary options;
    if (!ConvertFromV8(isolate, val, &options))
      return false;
    options.Get("origin", &out->origin);
    std::vector<std::string> types;
    if (options.Get("storages", &types))
      out->storage_types = GetStorageMask(types);
    if (options.Get("quotas", &types))
      out->quota_types = GetQuotaMask(types);
    return true;
  }
};
template<>
struct Converter<net::ProxyConfig> {
  static bool FromV8(v8::Isolate* isolate,
                     v8::Local<v8::Value> val,
                     net::ProxyConfig* out) {