function overrideDrmAndManifest(storage, drm, manifest) {
    storage.parseManifest = () => Promise.resolve(manifest);
    storage.createDrmEngine = () => Promise.resolve(drm);
  }
@param {!shaka.offline.Storage} storage
@param {!shaka.drm.DrmEngine} drm
@param {shaka.extern.Manifest} manifest