- 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_download_item.cc
v8::Isolate* isolate, content::DownloadItem* item) {
  auto existing = TrackableObject::FromWrappedClass(isolate, item);
  if (existing)
    return mate::CreateHandle(isolate, static_cast<DownloadItem*>(existing));
  auto handle = mate::CreateHandle(isolate, new DownloadItem(isolate, item));
  
  g_download_item_objects[handle->weak_map_id()] =
      v8::Global<v8::Object>(isolate, handle.ToV8());
  return handle;
}
}  
}  
namespace {
void Initialize(v8::Local<v8::Object> exports, v8::Local<v8::Value> unused,
                v8::Local<v8::Context> context, void* priv) {
  v8::Isolate* isolate = context->GetIsolate();
  mate::Dictionary(isolate, exports)
      .Set("DownloadItem",
           atom::api::DownloadItem::GetConstructor(isolate)->GetFunction());
}
}  
NODE_MODULE_CONTEXT_AWARE_BUILTIN(atom_browser_download_item, Initialize);