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
ClearStorageDataOptions options;
  args->GetNext(&options);
  base::Closure callback;
  if (!args->GetNext(&callback)) {
    args->ThrowError();
    return;
  }
  auto storage_partition =
      content::BrowserContext::GetStoragePartition(browser_context(), nullptr);
  storage_partition->ClearData(
      options.storage_types, options.quota_types, options.origin,
      content::StoragePartition::OriginMatcherFunction(),
      base::Time(), base::Time::Max(), callback);
}
void Session::FlushStorageData() {
  auto storage_partition =
      content::BrowserContext::GetStoragePartition(browser_context(), nullptr);
  storage_partition->Flush();
}
void Session::SetProxy(const net::ProxyConfig& config,
                       const base::Closure& callback) {
  auto getter = browser_context_->GetRequestContext();
  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
      base::Bind(&SetProxyInIO, base::Unretained(getter), config, callback));
}
void Session::SetDownloadPath(const base::FilePath& path) {