remove type annotation from AttributeMapWrapper

pkg/template_binding/test/custom_element_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 template_binding.test.custom_element_bindings_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:template_binding/template_binding.dart';
 import 'package:observe/observe.dart' show toObservable;
@@ skipping 191 matching lines @@
     if (property == 'scary-monster') node.scaryMonster = newValue;
   }
 }
 
 
 /**
  * Demonstrates a custom element can override attributes []= and remove.
  * and see changes that the data binding system is making to the attributes.
  */
 class WithAttrsCustomElement extends HtmlElement {
-  AttributeMapWrapper<String, String> _attributes;
+  AttributeMapWrapper _attributes;
 
   factory WithAttrsCustomElement() =>
       new Element.tag('with-attrs-custom-element');
 
   WithAttrsCustomElement.created() : super.created() {
     _attributes = new AttributeMapWrapper(super.attributes);
   }
 
   get attributes => _attributes;
 }
@@ skipping 23 matching lines @@
 
   void addAll(Map<K, V> other) => _map.addAll(other);
   void clear() => _map.clear();
   void forEach(void f(K key, V value)) => _map.forEach(f);
   Iterable<K> get keys => _map.keys;
   Iterable<V> get values => _map.values;
   int get length => _map.length;
   bool get isEmpty => _map.isEmpty;
   bool get isNotEmpty => _map.isNotEmpty;
 }