Restore implementation class for DOMStringMap.

lib/dom/src/native_DOMImplementation.dart

 // Copyright (c) 2012, 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.
 
 class _Utils {
   static List convertToList(List list) {
     // FIXME: [possible optimization]: do not copy the array if Dart_IsArray is fine w/ it.
     final length = list.length;
     List result = new List(length);
     result.copyFrom(list, 0, 0, length);
@@ skipping 69 matching lines @@
 
 class _LocationCrossFrameImpl extends _DOMWrapperBase implements Location {
   _LocationCrossFrameImpl();
 
   // Fields.
   void set href(String) native "Location_href_Setter";
 
   // Implementation support.
   String get typeName() => "Location";
 }
+
+class _DOMStringMapImpl extends _DOMWrapperBase implements Map<String, String> {
+  _DOMStringMapImpl();
+
+  bool containsValue(String value) => Maps.containsValue(this, value);
+  bool containsKey(String key) native "DOMStringMap_containsKey_Callback";
+  String operator [](String key) native "DOMStringMap_item_Callback";
+  void operator []=(String key, String value) native "DOMStringMap_setItem_Callback";
+  String putIfAbsent(String key, String ifAbsent()) => Maps.putIfAbsent(this, key, ifAbsent);
+  String remove(String key) native "DOMStringMap_remove_Callback";
+  void clear() => Maps.clear(this);
+  void forEach(void f(String key, String value)) => Maps.forEach(this, f);
+  Collection<String> getKeys() native "DOMStringMap_getKeys_Callback";
+  Collection<String> getValues() => Maps.getValues(this);
+  int get length() => Maps.length(this);
+  bool isEmpty() => Maps.isEmpty(this);
+}