Fix unresolved classes issues in dart:io.

sdk/lib/io/http_impl.dart

 // Copyright (c) 2012, 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.
 
 // The close queue handles graceful closing of HTTP connections. When
 // a connection is added to the queue it will enter a wait state
 // waiting for all data written and possibly socket shutdown from
 // peer.
 class _CloseQueue {
   _CloseQueue() : _q = new Set<_HttpConnectionBase>();
@@ skipping 2268 matching lines @@
 
 
 class _HttpClientDigestCredentials implements HttpClientDigestCredentials {
   _HttpClientDigestCredentials(this.username,
                                this.password);
 
   _AuthenticationScheme get scheme => _AuthenticationScheme.DIGEST;
 
   void authorize(_Credentials credentials, HttpClientRequest request) {
     // TODO(sgjesse): Implement!!!
-    throw new UnsupportedOperationException();
+    throw new UnsupportedError("Digest authentication not yet supported");
   }
 
   String username;
   String password;
 }
 
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }