Add "contains" method to Collection.

lib/html/src/Isolates.dart

Index: lib/html/src/Isolates.dart
diff --git a/lib/html/src/Isolates.dart b/lib/html/src/Isolates.dart
index b378b91d6ede233466c67af3b827fbb1f643f3ed..d5a297af9ed1e41546ce9387fe754b64bde6938e 100644
--- a/lib/html/src/Isolates.dart
+++ b/lib/html/src/Isolates.dart
@@ -84,7 +84,7 @@ class _RemoteSendPortSync implements SendPortSync {
   }
 
   static _call(int isolateId, int portId, var message) {
-    var target = 'dart-port-$isolateId-$portId'; 
+    var target = 'dart-port-$isolateId-$portId';
     // TODO(vsm): Make this re-entrant.
     // TODO(vsm): Set this up set once, on the first call.
     var source = '$target-result';
@@ -149,13 +149,13 @@ class ReceivePortSync {
   static int get _isolateId {
     // TODO(vsm): Make this coherent with existing isolate code.
     if (_cachedIsolateId == null) {
-      _cachedIsolateId = _getNewIsolateId();      
+      _cachedIsolateId = _getNewIsolateId();
     }
     return _cachedIsolateId;
   }
 
   static String _getListenerName(isolateId, portId) =>
-      'dart-port-$isolateId-$portId'; 
+      'dart-port-$isolateId-$portId';
   String get _listenerName => _getListenerName(_isolateId, _portId);
 
   void receive(callback(var message)) {