Generate tear-off closures dynamically.

dart/pkg/observe/test/path_observer_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.
 
 import 'package:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 import 'observe_test_utils.dart';
 
 // This file contains code ported from:
 // https://github.com/rafaelw/ChangeSummary/blob/master/tests/test.js
@@ skipping 265 matching lines @@
   @reflectable get foo {
     getFooCalled++;
     (this as dynamic).bar;
   }
   @reflectable set foo(value) {
     setFooCalled.add(value);
     (this as dynamic).bar = value;
   }
 }
 
+@reflectable
 class NoSuchMethodModel {
   var _foo = 42;
   List log = [];
 
   noSuchMethod(Invocation invocation) {
     final name = invocation.memberName;
     log.add(name);
     if (name == #foo && invocation.isGetter) return _foo;
     if (name == const Symbol('foo=')) {
       _foo = invocation.positionalArguments[0];
@@ skipping 45 matching lines @@
 
 class WatcherModel extends Observable {
   // TODO(jmesserly): dart2js does not let these be on the same line:
   // @observable var a, b, c;
   @observable var a;
   @observable var b;
   @observable var c;
 
   WatcherModel();
 }