Fix polymer_expression binding bug with observable list

pkg/polymer_expressions/test/bindings_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 bindings_test;
 
 import 'dart:async';
 import 'dart:html';
 
 import 'package:observe/observe.dart';
@@ skipping 112 matching lines @@
         // ... or on the next animation frame.
         expect(el.selectionStart, 4);
         expect(el.selectionEnd, 4);
       }).then(_afterTimeout).then((_) {
         // ... or later.
         expect(el.selectionStart, 4);
         expect(el.selectionEnd, 4);
       });
     });
 
+    test('detects changes to ObservableList', () {
+      var list = new ObservableList.from([1, 2, 3]);
+      var template = templateBind(new Element.html(
+          '<template>{{x[1]}}</template>'));
+      var model = new NotifyModel(list);
+      testDiv.append(template.createInstance(model, new PolymerExpressions()));
+
+      return new Future(() {
+        expect(testDiv.text, '2');
+        list[1] = 10;
+      }).then(_nextMicrotask).then((_) {
+        expect(testDiv.text, '10');
+        list[1] = 11;
+      }).then(_nextMicrotask).then((_) {
+        expect(testDiv.text, '11');
+        list[0] = 9;
+      }).then(_nextMicrotask).then((_) {
+        expect(testDiv.text, '11');
+        list.removeAt(0);
+      }).then(_nextMicrotask).then((_) {
+        expect(testDiv.text, '3');
+        list.add(90);
+        list.removeAt(0);
+      }).then(_nextMicrotask).then((_) {
+        expect(testDiv.text, '90');
+      });
+    });
 
     test('detects changes to ObservableMap keys/values', () {
       var map = new ObservableMap.from({'a': 1, 'b': 2});
       var template = templateBind(new Element.html('<template>'
           '<template repeat="{{k in x.keys}}">{{k}}:{{x[k]}},</template>'
           '</template>'));
       var model = new NotifyModel(map);
       testDiv.append(template.createInstance(model, new PolymerExpressions()));
 
       return new Future(() {
@@ skipping 16 matching lines @@
 @reflectable
 class NotifyModel extends ChangeNotifier {
   var _x;
   NotifyModel([this._x]);
 
   get x => _x;
   set x(value) {
     _x = notifyPropertyChange(#x, _x, value);
   }
 }