Copy the web socket stuff from http_parser.

lib/src/exception.dart

Index: lib/src/exception.dart
diff --git a/lib/src/exception.dart b/lib/src/exception.dart
new file mode 100644
index 0000000000000000000000000000000000000000..d06dc60e9db21eda7179cdcfeb77ff991b450890
--- /dev/null
+++ b/lib/src/exception.dart
@@ -0,0 +1,19 @@
+// 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 a [WebSocketChannel].
+class WebSocketChannelException implements Exception {
+  final String message;
+
+  /// The exception that caused this one, if available.
+  final inner;
+
+  WebSocketChannelException([this.message, this.inner]);
+
+  String toString() => message == null
+      ? "WebSocketChannelException" :
+        "WebSocketChannelException: $message";
+}