Add support for Websocket protocols.

tests/standalone/io/web_socket_protocol_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.
+//
+// VMOptions=
+// VMOptions=--short_socket_read
+// VMOptions=--short_socket_write
+// VMOptions=--short_socket_read --short_socket_write
+
+import "package:expect/expect.dart";
+import "dart:async";
+import "dart:io";
+
+
+testEmptyProtocol() {
+  HttpServer.bind("127.0.0.1", 0).then((server) {
+    server.listen((request) {
+      WebSocketTransformer.upgrade(request).then((websocket) {
+        websocket.close();
+      });
+    });
+    WebSocket.connect("ws://127.0.0.1:${server.port}/",
+                      protocols: []).then((client) {
+      Expect.isNull(client.protocol);
+      client.close();
+      server.close();
+    });
+  });
+}
+
+
+testProtocol(List<String> protocols, String used) {
+  selector(List<String> receivedProtocols) {
+    Expect.listEquals(protocols, receivedProtocols);
+    return used;
+  }
+  HttpServer.bind("127.0.0.1", 0).then((server) {
+    server.listen((request) {
+      WebSocketTransformer.upgrade(request,
+                                   protocolSelector: selector)
+        .then((websocket) {
+          Expect.equals(used, websocket.protocol);
+          websocket.close();
+        });
+    });
+    WebSocket.connect("ws://127.0.0.1:${server.port}/",
+                      protocols: protocols).then((client) {
+      Expect.equals(used, client.protocol);
+      client.close();
+      server.close();
+    });
+  });
+}
+
+
+testProtocolHandler() {
+  selector(List<String> receivedProtocols) {
+    throw "error";
+  }
+  HttpServer.bind("127.0.0.1", 0).then((server) {
+    server.listen((request) {
+      WebSocketTransformer.upgrade(request,
+                                   protocolSelector: selector)
+        .then((websocket) {
+          Expect.fail('error expected');
+        }, onError: (error) {
+          Expect.equals('error', error);
+        });
+    });
+    WebSocket.connect("ws://127.0.0.1:${server.port}/",
+                      protocols: ["v1.example.com"])
+      .then((client) {
+        Expect.fail('error expected');
+      }, onError: (error) {
+        server.close();
+      });
+  });
+}
+
+
+void main() {
+  testEmptyProtocol();
+  testProtocol(["v1.example.com", "v2.example.com"], "v1.example.com");
+  testProtocol(["v1.example.com", "v2.example.com"], "v2.example.com");
+  testProtocolHandler();
+}
+