- 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
uint32_t quota_mask = 0;
  for (const auto& it : quota_types) {
    auto type = base::ToLowerASCII(it);
    if (type == "temporary")
      quota_mask |= StoragePartition::QUOTA_MANAGED_STORAGE_MASK_TEMPORARY;
    else if (type == "persistent")
      quota_mask |= StoragePartition::QUOTA_MANAGED_STORAGE_MASK_PERSISTENT;
    else if (type == "syncable")
      quota_mask |= StoragePartition::QUOTA_MANAGED_STORAGE_MASK_SYNCABLE;
  }
  return quota_mask;
}
void SetUserAgentInIO(scoped_refptr<net::URLRequestContextGetter> getter,
                      const std::string& accept_lang,
                      const std::string& user_agent) {
  getter->GetURLRequestContext()->set_http_user_agent_settings(
      new net::StaticHttpUserAgentSettings(
          net::HttpUtil::GenerateAcceptLanguageHeader(accept_lang),
          user_agent));
}
}  
namespace mate {
template<>
struct Converter<ClearStorageDataOptions> {
  static bool FromV8(v8::Isolate* isolate,