We missed this because Flow wasn't being run properly on Travis but now that it is, it's clear that #7716 introduced a bunch of new Flow failures. Most of these shouldn't be too bad and I like to say "you break it you buy it" so this one is for you @Aweary :)

There were a couple other pre-existing Flow issues that @vjeux is going to fix, so mostly this should just be the TestRenderer issues.

var tag = element.type;
  validateDangerousTag(tag);
  this._currentElement = element;
  this._tag = tag.toLowerCase();
  this._namespaceURI = null;
  this._renderedChildren = null;
  this._previousStyle = null;
  this._previousStyleCopy = null;
  this._hostNode = null;
  this._hostParent = null;
  this._rootNodeID = 0;
  this._domID = 0;
  this._hostContainerInfo = null;
  this._wrapperState = null;
  this._topLevelWrapper = null;
  this._flags = 0;
  if (__DEV__) {
    this._ancestorInfo = null;
    setAndValidateContentChildDev.call(this, null);
  }
}
ReactDOMComponent.displayName = 'ReactDOMComponent';
ReactDOMComponent.Mixin = {
  /**
   * Generates root tag markup then recurses. This method has side effects and
   * is not idempotent.
   *
   * @internal
   * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
   * @param {?ReactDOMComponent} the parent component instance