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 mountImage;
    if (transaction.useCreateElement) {
      var ownerDocument = hostContainerInfo._ownerDocument;
      var el;
      if (namespaceURI === DOMNamespaces.html) {
        if (this._tag === 'script') {
          
          
          var div = ownerDocument.createElement('div');
          var type = this._currentElement.type;
          div.innerHTML = `<${type}></${type}>`;
          el = div.removeChild(div.firstChild);
        } else if (props.is) {
          el = ownerDocument.createElement(this._currentElement.type, props.is);
        } else {
          
          
          
          el = ownerDocument.createElement(this._currentElement.type);
        }
      } else {
        el = ownerDocument.createElementNS(
          namespaceURI,
          this._currentElement.type
        );
      }
      ReactDOMComponentTree.precacheNode(this, el);
      this._flags |= Flags.hasCachedChildNodes;
      if (!this._hostParent) {
        DOMPropertyOperations.setAttributeForRoot(el);