code: private static boolean isJscompPolyfill(Node n) {
      switch (n.getToken()) {
        case NAME:
          // Need to work correctly after CollapseProperties.
          return n.getString().equals("$jscomp$polyfill") && n.getNext().isString();
        case GETPROP:
          // Need to work correctly without CollapseProperties.
          return n.getLastChild().getString().equals("polyfill")
              && n.getFirstChild().isName()
              && n.getFirstChild().getString().equals("$jscomp")
              && n.getNext().isString();
        default:
          return false;
      }
    }
docs: Checks whether this is a recognizable call to $jscomp.polyfill.