function instantiateReactComponent(descriptor) {

  // TODO: Make warning
  // if (__DEV__) {
    ("production" !== "development" ? invariant(
      isValidComponentDescriptor(descriptor),
      'Only React Components are valid for mounting.'
    ) : invariant(isValidComponentDescriptor(descriptor)));
  // }

  return new descriptor.type(descriptor);
}
Given a `componentDescriptor` create an instance that will actually be
mounted. Currently it just extracts an existing clone from composite
components but this is an implementation detail which will change.

@param {object} descriptor
@return {object} A new instance of componentDescriptor's constructor.
@protected