- 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
std::unique_ptr<brightray::DevToolsNetworkConditions> conditions;
  browser_context_->network_controller_handle()->SetNetworkState(
      devtools_network_emulation_client_id_, std::move(conditions));
  browser_context_->network_delegate()->SetDevToolsNetworkEmulationClientId(
      std::string());
}
void Session::SetCertVerifyProc(v8::Local<v8::Value> val,
                                mate::Arguments* args) {
  AtomCertVerifier::VerifyProc proc;
  if (!(val->IsNull() || mate::ConvertFromV8(args->isolate(), val, &proc))) {
    args->ThrowError("Must pass null or function");
    return;
  }
  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
      base::Bind(&SetCertVerifyProcInIO,
                 make_scoped_refptr(browser_context_->GetRequestContext()),
                 proc));
}
void Session::SetPermissionRequestHandler(v8::Local<v8::Value> val,