code: private static boolean isPolyfillDefinition(Node callee) {
      // If the callee is just $jscomp.polyfill then it's easy.
      if (callee.matchesQualifiedName("$jscomp.polyfill")
          || callee.matchesQualifiedName("$jscomp$polyfill")) {
        return true;
      }
      // It's possible that the function has been inlined, so look for
      // a four-parameter function with parameters who have the correct
      // prefix (since a disambiguate suffix may have been added).
      if (callee.isFunction()) {
        Node paramList = callee.getSecondChild();
        Node param = paramList.getFirstChild();
        if (paramList.hasXChildren(4)) {
          for (String name : POLYFILL_PARAMETERS) {
            if (!param.isName() || !param.getString().startsWith(name)) {
              return false;
            }
            param = param.getNext();
          }
          return true;
        }
      }
      return false;
    }
docs: Checks whether the node is (or was) a call to $jscomp.polyfill.