Remove Collection, Collections and clean up List/Set/Queue implementations of retain/remove.

tools/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.
 
 part of html;
 
 class _Utils {
   static double dateTimeToDouble(DateTime dateTime) =>
       dateTime.millisecondsSinceEpoch.toDouble();
   static DateTime doubleToDateTime(double dateTime) {
@@ skipping 108 matching lines @@
   _DOMStringMap.internal();
 
   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> get keys native "DOMStringMap_getKeys_Callback";
-  Collection<String> get values => Maps.getValues(this);
+  Iterable<String> get keys native "DOMStringMap_getKeys_Callback";
+  Iterable<String> get values => Maps.getValues(this);
   int get length => Maps.length(this);
   bool get isEmpty => Maps.isEmpty(this);
 }
 
 final Future<SendPort> __HELPER_ISOLATE_PORT =
     spawnDomFunction(_helperIsolateMain);
 
 // Tricky part.
 // Once __HELPER_ISOLATE_PORT gets resolved, it will still delay in .then
 // and to delay Timer.run is used. However, Timer.run will try to register
@@ skipping 99 matching lines @@
   }
 
   _send(msg) {
     _sendToHelperIsolate(msg, _sendPort);
   }
 }
 
 get _pureIsolateTimerFactoryClosure =>
     ((int milliSeconds, void callback(Timer time), bool repeating) =>
         new _PureIsolateTimer(milliSeconds, callback, repeating));