- Electron version: 1.4.3
- Operating system:  @win7
- description:

working on a download app with electron and angular. 
By using webContents.downloadUrl, webContents.session.on('will-download', handler) I can make download function work well, however, I could not find a api to save download progress before closing electron app so that I can restore download when this app is started next time.

Excepted Result:
1. user click 'download' button to download a 1G file.
2. after 500M is downloaded, user quit the app
3. one hour later, user open this app again, and downloading can automatically be restored

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->url_request_context_getter();
    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,