Add support for Websocket protocols.

sdk/lib/io/websocket.dart

Index: sdk/lib/io/websocket.dart
diff --git a/sdk/lib/io/websocket.dart b/sdk/lib/io/websocket.dart
index a3f2b258e4d97fbf4e845491832d583ef7d9118f..f9229ae8e5afc6b9d32de18b27b0f5ddafc1b10f 100644
--- a/sdk/lib/io/websocket.dart
+++ b/sdk/lib/io/websocket.dart
@@ -53,7 +53,9 @@ abstract class WebSocketStatus {
  */
 abstract class WebSocketTransformer
     implements StreamTransformer<HttpRequest, WebSocket> {
-  factory WebSocketTransformer() => new _WebSocketTransformerImpl();
+
+  factory WebSocketTransformer({protocolSelector(List<String> protocols)})
+      => new _WebSocketTransformerImpl(protocolSelector);
 
   /**
    * Upgrades a [HttpRequest] to a [WebSocket] connection. If the
@@ -62,8 +64,9 @@ abstract class WebSocketTransformer
    * future will complete with the [WebSocket] when the upgrade pocess
    * is complete.
    */
-  static Future<WebSocket> upgrade(HttpRequest request) {
-    return _WebSocketTransformerImpl._upgrade(request);
+  static Future<WebSocket> upgrade(HttpRequest request,
+                                   {protocolSelector(List<String> protocols)}) {
+    return _WebSocketTransformerImpl._upgrade(request, protocolSelector);
   }
 
   /**
@@ -92,11 +95,11 @@ abstract class WebSocket implements Stream, StreamSink {
 
   /**
    * Create a new web socket connection. The URL supplied in [url]
-   * must use the scheme [:ws:] or [:wss:]. The [protocols] argument is either
-   * a [:String:] or [:List<String>:] specifying the subprotocols the
-   * client is willing to speak.
+   * must use the scheme [:ws:] or [:wss:]. The [protocols] argument is
+   * specifying the subprotocols the client is willing to speak.
    */
-  static Future<WebSocket> connect(String url, [protocols]) =>
+  static Future<WebSocket> connect(String url,
+                                   {List<String> protocols: const []}) =>
       _WebSocketImpl.connect(url, protocols);
 
   /**