function setID(node, id) {
  var oldID = internalGetID(node);
  if (oldID !== id) {
    delete nodeCache[oldID];
  }
  node.setAttribute(ATTR_NAME, id);
  nodeCache[id] = node;
}
Sets the React-specific ID of the given node.

@param {DOMElement} node The DOM node whose ID will be set.
@param {string} id The value of the ID attribute.