Unify dart:async and pub/io.dart TimeoutException classes.

sdk/lib/_internal/pub/lib/src/command/serve.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.
 
 library pub.command.serve;
 
-import 'dart:async' hide TimeoutException;
+import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 import '../barback/dart_forwarding_transformer.dart';
 import '../barback/dart2js_transformer.dart';
 import '../barback/pub_package_provider.dart';
 import '../barback.dart' as barback;
 import '../command.dart';
 import '../entrypoint.dart';
 import '../exit_codes.dart' as exit_codes;
@@ skipping 106 matching lines @@
         if (!completer.isCompleted) completer.completeError(error, stackTrace);
       });
 
       log.message("Serving ${entrypoint.root.name} "
           "on http://$hostname:${server.port}");
 
       return completer.future;
     });
   }
 }