This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
current: Fiber | null,
  workInProgress: Fiber,
  renderLanes: Lanes,
) {
  const nextChildren = workInProgress.pendingProps.children;
  reconcileChildren(current, workInProgress, nextChildren, renderLanes);
  return workInProgress.child;
}
function updateProfiler(
  current: Fiber | null,
  workInProgress: Fiber,
  renderLanes: Lanes,
) {
  if (enableProfilerTimer) {
    workInProgress.flags |= Update;
    if (enableProfilerCommitHooks) {
      
      
      const stateNode = workInProgress.stateNode;
      stateNode.effectDuration = 0;
      stateNode.passiveEffectDuration = 0;
    }
  }
  const nextProps = workInProgress.pendingProps;
  const nextChildren = nextProps.children;
  reconcileChildren(current, workInProgress, nextChildren, renderLanes);
  return workInProgress.child;
}
function markRef(current: Fiber | null, workInProgress: Fiber) {