Sanitize headers in Proxy Authentication Required responses

BUG=431504

Review URL: https://codereview.chromium.org/769043003

Cr-Commit-Position: refs/heads/master@{#310014}
  websocket_stream_create_helper() const {
    return websocket_stream_create_helper_;
  }

  websocket_stream_create_helper() const {
    return websocket_stream_create_helper_;
  }
