code: public WebSocket addHeader(String name, String value)
      {
          mHandshakeBuilder.addHeader(name, value);
  
          return this;
      }
docs: Add a pair of extra HTTP header.
  
  @param name
  An HTTP header name. When {@code null} or an empty
  string is given, no header is added.
  
  @param value
  The value of the HTTP header.
  
  @return
  {@code this} object.