Split dart:builtin into dart:builtin and dart:io.

samples/chat/chat_server_lib.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 #library("chat_server");
+#import("dart:io");
 #import("http.dart");
 #import("../../client/json/dart_json.dart");
 
 typedef void RequestHandler(HTTPRequest request, HTTPResponse response);
 
 class ChatServer extends IsolatedServer {
   ChatServer() : super() {
     addHandler("/",
                (HTTPRequest request, HTTPResponse response) =>
                    redirectPageHandler(
@@ skipping 722 matching lines @@
     }
   }
 
   int _timeRange;
   List<int> _buckets;
   int _currentBucket;
   int _currentBucketTime;
   num _bucketTimeRange;
   int _sum;
 }