code: public void windowUpdateRatio(Http2Stream stream, float ratio) throws Http2Exception {
          assert ctx != null && ctx.executor().inEventLoop();
          checkValidRatio(ratio);
          FlowState state = state(stream);
          state.windowUpdateRatio(ratio);
          state.writeWindowUpdateIfNeeded();
      }
docs: The window update ratio is used to determine when a window update must be sent. If the ratio
  of bytes processed since the last update has meet or exceeded this ratio then a window update will
  be sent. This window update ratio will only be applied to {@code streamId}.
  <p>
  Note it is the responsibly of the caller to ensure that the the
  initial {@code SETTINGS} frame is sent before this is called. It would
  be considered a {@link Http2Error#PROTOCOL_ERROR} if a {@code WINDOW_UPDATE}
  was generated by this method before the initial {@code SETTINGS} frame is sent.
  @param stream the stream for which {@code ratio} applies to.
  @param ratio the ratio to use when checking if a {@code WINDOW_UPDATE} is determined necessary.
  @throws Http2Exception If a protocol-error occurs while generating {@code WINDOW_UPDATE} frames