Fix internal NSM helper to use a Dart Symbol

lib/runtime/dart/_runtime.js

 dart_library.library('dart/_runtime', null, /* Imports */[
 ], /* Lazy imports */[
   'dart/core',
   'dart/_interceptors',
   'dart/_js_helper',
   'dart/async',
   'dart/collection'
 ], function(exports, core, _interceptors, _js_helper, async, collection) {
   'use strict';
   function mixin(base, ...mixins) {
@@ skipping 408 matching lines @@
     let names = getOwnPropertyNames(opts);
     if (names.length == 0) return false;
     for (var name of names) {
       if (!hasOwnProperty.call(type.named, name)) {
         return false;
       }
       if (!instanceOfOrNull(opts[name], type.named[name])) return false;
     }
     return true;
   }
+  function _dartSymbol(name) {
+    return const_(core.Symbol.new(name.toString()));
+  }
   function throwNoSuchMethod(obj, name, pArgs, nArgs, extras) {
-    throw_(new core.NoSuchMethodError(obj, name, pArgs, nArgs, extras));
+    throw_(new core.NoSuchMethodError(obj, _dartSymbol(name), pArgs, nArgs, extras));
   }
   function throwNoSuchMethodFunc(obj, name, pArgs, opt_func) {
     if (obj === void 0) obj = opt_func;
     throwNoSuchMethod(obj, name, pArgs);
   }
   function checkAndCall(f, ftype, obj, args, name) {
     let originalFunction = f;
     if (!(f instanceof Function)) {
       if (f != null) {
         ftype = getMethodType(f, 'call');
@@ skipping 876 matching lines @@
   exports.copyProperties = copyProperties;
   exports.export = export_;
   exports.defineLazyClass = defineLazyClass;
   exports.defineLazyProperties = defineLazyProperties;
   exports.defineLazyClassGeneric = defineLazyClassGeneric;
   exports.as = as_;
   exports.is = is_;
   exports.global = global_;
   exports.JsSymbol = JsSymbol;
 });