Fix memory leak in Windows Browsers

- This version includes changes from this pull request of
  AwesomeWebSocket:

  https://github.com/glg/awesome-websocket/pull/7

- This version includes changes from this pull request of
  core-custom-event-client:

  https://github.com/Custom-Elements/core-custom-event-client/pull/3

- This CRX has been tested on Mac (OS X) and Windows