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.

componentInstance,
    transaction,
  ) {
  var image = ReactReconciler.mountComponent(
    componentInstance,
    transaction,
    null,
    null,
    emptyObject
  );
  componentInstance._renderedComponent._topLevelWrapper = componentInstance;
  return image;
}
/**
 * Batched mount.
 *
 * @param {ReactComponent} componentInstance The instance to mount.
 * @param {number} rootID ID of the root node.
 * @param {number} containerTag container element to mount into.
 */
function batchedMountComponentIntoNode(