Add library mapping.

dart/frog/leg/io/io.dart

Index: dart/frog/leg/io/io.dart
diff --git a/dart/frog/leg/io/io.dart b/dart/frog/leg/io/io.dart
deleted file mode 100644
index 541ef826acb62b11e767b84f236f91665ce12e9e..0000000000000000000000000000000000000000
--- a/dart/frog/leg/io/io.dart
+++ /dev/null
@@ -1,15 +0,0 @@
-// Copyright (c) 2011, 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("io");
-
-#import("dart:io");
-
-String join(List<String> strings) => Strings.join(strings, '/');
-
-String getCurrentDirectory() {
-  String dir = new File(".").fullPathSync();
-  if (dir.endsWith("/")) return dir;
-  return "$dir/";
-}