Clean up dart:io exceptions.

sdk/lib/io/http.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.
 
 part of dart.io;
 
 /**
  * HTTP status codes.
  */
 abstract class HttpStatus {
@@ skipping 1335 matching lines @@
  * unparsed data already read from the socket. This unparsed data
  * together with the detached socket is returned in an instance of
  * this class.
  */
 abstract class DetachedSocket {
   Socket get socket;
   List<int> get unparsedData;
 }
 
 
-class HttpException implements Exception {
+class HttpException implements IOException {
+  final String message;
+
   const HttpException([String this.message = ""]);
+
   String toString() => "HttpException: $message";
-  final String message;
 }
 
 
-class RedirectException extends HttpException {
-  const RedirectException(String message,
-                          List<RedirectInfo> this.redirects) : super(message);
+class RedirectException implements HttpException {
+  final String message;
   final List<RedirectInfo> redirects;
+
+  const RedirectException(String this.message,
+                          List<RedirectInfo> this.redirects);
+
+  String toString() => "RedirectException: $message";
 }
-
-
-class RedirectLimitExceededException extends RedirectException {
-  const RedirectLimitExceededException(List<RedirectInfo> redirects)
-      : super("Redirect limit exceeded", redirects);
-}
-
-
-class RedirectLoopException extends RedirectException {
-  const RedirectLoopException(List<RedirectInfo> redirects)
-      : super("Redirect loop detected", redirects);
-}