Change MirrorSystem.libraries to Map<Uri, String>

sdk/lib/_internal/compiler/implementation/filenames.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.
 
 library filenames;
 
 import 'dart:io';
 import 'dart:uri';
 
 // TODO(ahe): This library should be replaced by a general
 // path-munging library.
 //
 // See also:
 // http://blogs.msdn.com/b/ie/archive/2006/12/06/file-uris-in-windows.aspx
 
 String nativeToUriPath(String filename) {
   return new Path(filename).toString();
 }
 
 String uriPathToNative(String path) {
   return new Path(path).toNativePath();
 }
 
-Uri getCurrentDirectory() {
-  final String dir = nativeToUriPath(new File('.').fullPathSync());
-  return new Uri.fromComponents(scheme: 'file', path: appendSlash(dir));
-}
+final Uri currentDirectory = new Uri.fromComponents(
+    scheme: 'file',
+    path: appendSlash(nativeToUriPath(new File('.').fullPathSync())));
 
 String appendSlash(String path) => path.endsWith('/') ? path : '$path/';