Use Object.create instead of a tmp-function.

dart/sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // Copyright (c) 2013, 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.
 
 library _js_helper;
 
 import 'shared/embedded_names.dart' show
     ALL_CLASSES,
     GET_ISOLATE_TAG,
     INTERCEPTED_NAMES,
@@ skipping 1952 matching lines @@
     // BoundClosure.  For this, we need to create an object whose prototype is
     // the prototype is either TearOffClosure.prototype or
     // BoundClosure.prototype, respectively in pseudo JavaScript code. The
     // simplest way to access the JavaScript construction function of a Dart
     // class is to create an instance and access its constructor property.  The
     // newly created instance could in theory be used directly as the
     // prototype, but it might include additional fields that we don't need.
     // So we only use the new instance to access the constructor property and
     // use Object.create to create the desired prototype.
     var prototype = isStatic
-        // TODO(ahe): Safe to use Object.create?
         ? JS('TearOffClosure', 'Object.create(#.constructor.prototype)',
              new TearOffClosure())
         : JS('BoundClosure', 'Object.create(#.constructor.prototype)',
              new BoundClosure(null, null, null, null));
 
     JS('', '#.\$initialize = #', prototype, JS('', '#.constructor', prototype));
     var constructor = isStatic
         ? JS('', 'function(){this.\$initialize()}')
         : isCsp
             ? JS('', 'function(a,b,c,d) {this.\$initialize(a,b,c,d)}')
             : JS('',
                  'new Function("a","b","c","d",'
                      '"this.\$initialize(a,b,c,d);"+#)',
                  functionCounter++);
 
-    // TODO(ahe): Is it necessary to set the constructor property?
+    // It is necessary to set the constructor property, otherwise it will be
+    // "Object".
     JS('', '#.constructor = #', prototype, constructor);
 
     JS('', '#.prototype = #', constructor, prototype);
 
     // Create a closure and "monkey" patch it with call stubs.
     var trampoline = function;
     var isIntercepted = false;
     if (!isStatic) {
       if (JS('bool', '#.length == 1', jsArguments)) {
         // Intercepted call.
@@ skipping 1402 matching lines @@
   throw new MainError("No top-level function named 'main'.");
 }
 
 void badMain() {
   throw new MainError("'main' is not a function.");
 }
 
 void mainHasTooManyParameters() {
   throw new MainError("'main' expects too many parameters.");
 }