void FilterManager::callLowWatermarkCallbacks() {
  ASSERT(high_watermark_count_ > 0);
  --high_watermark_count_;
  for (auto watermark_callbacks : watermark_callbacks_) {
    watermark_callbacks->onBelowWriteBufferLowWatermark();
  }
}
void FilterManager::callLowWatermarkCallbacks() {
  ASSERT(high_watermark_count_ > 0);
  --high_watermark_count_;
  for (auto watermark_callbacks : watermark_callbacks_) {
    watermark_callbacks->onBelowWriteBufferLowWatermark();
  }
}