While working on the DevTools profiler, I've noticed that durations are sometimes incorrect. This seems to be vaguely related to high/low priority state updates. Need to track this down more so I'm filing an issue for myself.
tag: TypeOfWork,
  pendingProps: mixed,
  key: null | string,
  mode: TypeOfMode,
) {
  
  this.tag = tag;
  this.key = key;
  this.type = null;
  this.stateNode = null;
  
  this.return = null;
  this.child = null;
  this.sibling = null;
  this.index = 0;
  this.ref = null;
  this.pendingProps = pendingProps;
  this.memoizedProps = null;
  this.updateQueue = null;
  this.memoizedState = null;
  this.firstContextDependency = null;
  this.mode = mode;
  
  this.effectTag = NoEffect;
  this.nextEffect = null;
  this.firstEffect = null;