void Filter::DownstreamCallbacks::onBelowWriteBufferLowWatermark() {
  ASSERT(on_high_watermark_called_);
  on_high_watermark_called_ = false;
  // The downstream buffer has been drained. Resume reading from upstream.
  parent_.readDisableUpstream(false);
}
void Filter::DownstreamCallbacks::onBelowWriteBufferLowWatermark() {
  ASSERT(on_high_watermark_called_);
  on_high_watermark_called_ = false;
   
  parent_.readDisableUpstream(false);
}