code: func NewSpdyRoundTripperWithDialer(cfg roundTripperConfig) *SpdyRoundTripper {
  	return &SpdyRoundTripper{tlsConfig: cfg.tlsConfig, followRedirects: cfg.followRedirects, dialWithContext: cfg.dial, ctx: cfg.ctx, authCtx: cfg.authCtx, bearerToken: cfg.bearerToken}
  }
docs: // NewSpdyRoundTripperWithDialer creates a new SpdyRoundTripper that will use
  // the specified tlsConfig. This function is mostly meant for unit tests.