Clean up dart:io exceptions.

sdk/lib/io/http.dart

Index: sdk/lib/io/http.dart
diff --git a/sdk/lib/io/http.dart b/sdk/lib/io/http.dart
index 4ea77f72d75e5591bcb105d792c70036babb3d83..b05a5744d27af934c13bfd42e0781fda09244709 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -1353,27 +1353,21 @@ abstract class DetachedSocket {
 }
 
 
-class HttpException implements Exception {
-  const HttpException([String this.message = ""]);
-  String toString() => "HttpException: $message";
+class HttpException implements IOException {
   final String message;
-}
 
+  const HttpException([String this.message = ""]);
 
-class RedirectException extends HttpException {
-  const RedirectException(String message,
-                          List<RedirectInfo> this.redirects) : super(message);
-  final List<RedirectInfo> redirects;
+  String toString() => "HttpException: $message";
 }
 
 
-class RedirectLimitExceededException extends RedirectException {
-  const RedirectLimitExceededException(List<RedirectInfo> redirects)
-      : super("Redirect limit exceeded", redirects);
-}
+class RedirectException implements HttpException {
+  final String message;
+  final List<RedirectInfo> redirects;
 
+  const RedirectException(String this.message,
+                          List<RedirectInfo> this.redirects);
 
-class RedirectLoopException extends RedirectException {
-  const RedirectLoopException(List<RedirectInfo> redirects)
-      : super("Redirect loop detected", redirects);
+  String toString() => "RedirectException: $message";
 }