addLicenseRequestHeaders_(headers, requestType, request) {
    if (requestType != shaka.net.NetworkingEngine.RequestType.LICENSE) {
      return;
    }

    // Add these to the existing headers.  Do not clobber them!
    // For PlayReady, there will already be headers in the request.
    headers.forEach((value, key) => {
      request.headers[key] = value;
    });
  }
@param {!Map<string, string>} headers
@param {shaka.net.NetworkingEngine.RequestType} requestType
@param {shaka.extern.Request} request
@private