Add a WebSocketChannel class.

lib/src/web_socket/exception.dart

Index: lib/src/web_socket/exception.dart
diff --git a/lib/src/web_socket/exception.dart b/lib/src/web_socket/exception.dart
new file mode 100644
index 0000000000000000000000000000000000000000..87f61d8911f978b23090fff05e5a0ac591735f3b
--- /dev/null
+++ b/lib/src/web_socket/exception.dart
@@ -0,0 +1,16 @@
+// Copyright (c) 2016, 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.
+
+import 'channel.dart';
+
+/// An exception thrown by [WebSocketChannel].
+class CompatibleWebSocketException implements Exception {
+  final String message;
+
+  CompatibleWebSocketException([this.message]);
+
+  String toString() => message == null
+      ? "CompatibleWebSocketException" :
+        "CompatibleWebSocketException: $message";
+}