Some more removals of dart:utf.

utils/lib/file_system_vm.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.
 
 // TODO(terry): Investigate common library for file I/O shared between frog and tools.
 
 library file_system_vm;
+import 'dart:convert';
 import 'dart:io';
 import 'file_system.dart';
-import 'dart:utf';
 
 /** File system implementation using the vm api's. */
 class VMFileSystem implements FileSystem {
   void writeString(String path, String text) {
     var file = new File(path).openSync(mode: FileMode.WRITE);
     file.writeStringSync(text);
     file.closeSync();
   }
 
   String readAll(String filename) {
     var file = (new File(filename)).openSync();
     var length = file.lengthSync();
     var buffer = new List<int>(length);
     var bytes = file.readIntoSync(buffer, 0, length);
     file.closeSync();
-    return new String.fromCharCodes(new Utf8Decoder(buffer).decodeRest());
+    return UTF8.decode(bytes);
   }
 
   bool fileExists(String filename) {
     return new File(filename).existsSync();
   }
 
   void createDirectory(String path, [bool recursive = false]) {
     // TODO(rnystrom): Implement.
     throw 'createDirectory() is not implemented by VMFileSystem yet.';
   }
 
   void removeDirectory(String path, [bool recursive = false]) {
     // TODO(rnystrom): Implement.
     throw 'removeDirectory() is not implemented by VMFileSystem yet.';
   }
 }