function getReactRootElementInContainer(container) {
	  if (!container) {
	    return null;
	  }

	  if (container.nodeType === DOC_NODE_TYPE) {
	    return container.documentElement;
	  } else {
	    return container.firstChild;
	  }
	}
@param {DOMElement|DOMDocument} container DOM element that may contain
a React component
@return {?*} DOM element that may have the reactRoot ID, or null.