Maintain referential integrity of proxy instances in dart:js

tests/html/js_test.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 jsTest;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js';
 
@@ skipping 106 matching lines @@
   this.f3 = p3;
   this.f4 = p4;
   this.f5 = p5;
   this.f6 = p6;
   this.f7 = p7;
   this.f8 = p8;
   this.f9 = p9;
   this.f10 = p10;
   this.f11 = p11;
 }
+
+function identical(o1, o2) {
+  return o1 === o2;
+}
 """;
   document.body.append(script);
 }
 
 class Foo implements Serializable<JsObject> {
   final JsObject _proxy;
 
   Foo(num a) : this._proxy = new JsObject(context['Foo'], [a]);
 
   JsObject toJs() => _proxy;
 
   num get a => _proxy['a'];
   num bar() => _proxy.callMethod('bar');
 }
 
 class Color implements Serializable<String> {
   static final RED = new Color._("red");
   static final BLUE = new Color._("blue");
   String _value;
   Color._(this._value);
   String toJs() => this._value;
 }
 
+class TestDartObject {}
+
 main() {
   _injectJs();
   useHtmlConfiguration();
 
   test('context instances should be identical', () {
     var c1 = context;
     var c2 = context;
     expect(identical(c1, c2), isTrue);
   });
 
+  test('identical JS objects should have identical proxies', () {
+    var o1 = context['location'];
+    var o2 = context['location'];
+    expect(identical(o1, o2), isTrue);
+  });
+
+  test('identical JS functions should have identical proxies', () {
+    var f1 = context['Object'];
+    var f2 = context['Object'];
+    expect(identical(f1, f2), isTrue);
+  });
+
+  test('identical Dart objects should have identical proxies', () {
+    var o1 = new TestDartObject();
+    expect(context.callMethod('identical', [o1, o1]), isTrue);
+  });
+
+  test('identical Dart functions should have identical proxies', () {
+    var f1 = () => print("I'm a Function!");
+    expect(context.callMethod('identical', [f1, f1]), isTrue);
+  });
+
   test('read global field', () {
     expect(context['x'], equals(42));
     expect(context['y'], isNull);
   });
 
   test('read global field with underscore', () {
     expect(context['_x'], equals(123));
     expect(context['y'], isNull);
   });
 
@@ skipping 296 matching lines @@
     context['dartDate'] = date;
     expect(context['dartDate'], equals(date));
   });
 
   test('usage of Serializable', () {
     final red = Color.RED;
     context['color'] = red;
     expect(context['color'], equals(red._value));
   });
 }