static requestMediaKeySystemAccess(keySystem, supportedConfigurations) {
    shaka.log.debug('PatchedMediaKeysApple.requestMediaKeySystemAccess');
    goog.asserts.assert(this == navigator,
        'bad "this" for requestMediaKeySystemAccess');

    // Alias.
    const PatchedMediaKeysApple = shaka.polyfill.PatchedMediaKeysApple;
    try {
      const access = new PatchedMediaKeysApple.MediaKeySystemAccess(
          keySystem, supportedConfigurations);
      return Promise.resolve(/** @type {!MediaKeySystemAccess} */ (access));
    } catch (exception) {
      return Promise.reject(exception);
    }
  }
An implementation of navigator.requestMediaKeySystemAccess.
Retrieves a MediaKeySystemAccess object.

@this {!Navigator}
@param {string} keySystem
@param {!Array<!MediaKeySystemConfiguration>} supportedConfigurations
@return {!Promise<!MediaKeySystemAccess>}