- 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 storage_mask = 0;
  for (const auto& it : storage_types) {
    auto type = base::ToLowerASCII(it);
    if (type == "appcache")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_APPCACHE;
    else if (type == "cookies")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_COOKIES;
    else if (type == "filesystem")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_FILE_SYSTEMS;
    else if (type == "indexdb")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_INDEXEDDB;
    else if (type == "localstorage")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_LOCAL_STORAGE;
    else if (type == "shadercache")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_SHADER_CACHE;
    else if (type == "websql")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_WEBSQL;
    else if (type == "serviceworkers")
      storage_mask |= StoragePartition::REMOVE_DATA_MASK_SERVICE_WORKERS;
  }
  return storage_mask;
}
uint32_t GetQuotaMask(const std::vector<std::string>& quota_types) {