code: function createFiberRoot(containerInfo, isAsync, hydrate) {
    // Cyclic construction. This cheats the type system right now because
    // stateNode is any.
    var uninitializedFiber = createHostRootFiber(isAsync);
    var root = {
      current: uninitializedFiber,
      containerInfo: containerInfo,
      pendingChildren: null,
      pendingCommitExpirationTime: NoWork,
      finishedWork: null,
      context: null,
      pendingContext: null,
      hydrate: hydrate,
      remainingExpirationTime: NoWork,
      firstBatch: null,
      nextScheduledRoot: null
    };
    uninitializedFiber.stateNode = root;
    return root;
  }
docs: TODO: This should be lifted into the renderer.