fixes private named constructors

lib/runtime/dart_runtime.js

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 var dart, _js_helper;
 (function (dart) {
   'use strict';
 
   var defineProperty = Object.defineProperty;
   var getOwnPropertyDescriptor = Object.getOwnPropertyDescriptor;
@@ skipping 263 matching lines @@
   dart.assert = assert;
 
   function throw_(obj) { throw obj; }
   dart.throw_ = throw_;
 
   /**
    * Given a class and an initializer method name, creates a constructor
    * function with the same name. For example `new SomeClass.name(args)`.
    */
   function defineNamedConstructor(clazz, name) {
-    var shortName = name.startsWith('::') ? name.substring(2) : name;
     var proto = clazz.prototype;
-    var initMethod = proto[clazz.name + '$' + shortName];
+    var initMethod = proto[name];
     var ctor = function() { return initMethod.apply(this, arguments); }
     ctor.prototype = proto;
     clazz[name] = ctor;
   }
   dart.defineNamedConstructor = defineNamedConstructor;
 
   function stackTrace(exception) {
     throw new core.UnimplementedError();
   }
   dart.stackTrace = stackTrace;
@@ skipping 43 matching lines @@
   // of some sort, assuming we keep around `dynamic` at runtime.
   dart.dynamic = Object.create(null);
 
   dart.JsSymbol = Symbol;
 
   // TODO(jmesserly): hack to bootstrap the SDK
   _js_helper = _js_helper || {};
   _js_helper.checkNum = notNull;
 
 })(dart || (dart = {}));