Some more removals of dart:utf.

pkg/barback/lib/src/asset.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 barback.asset;
 
 import 'dart:async';
-import 'dart:convert' show Encoding, UTF8;
+import 'dart:convert';
 import 'dart:io';
-import 'dart:utf';
 
 import 'asset_id.dart';
 import 'utils.dart';
 
 /// A blob of content.
 ///
 /// Assets may come from the file system, or as the output of a [Transformer].
 /// They are identified by [AssetId].
 abstract class Asset {
   /// The ID for this asset.
@@ skipping 90 matching lines @@
 class _StringAsset extends Asset {
   final String _contents;
 
   _StringAsset(AssetId id, this._contents)
       : super(id);
 
   Future<String> readAsString({Encoding encoding}) =>
       new Future.value(_contents);
 
   Stream<List<int>> read() =>
-      new Future<List<int>>.value(encodeUtf8(_contents)).asStream();
+      new Future<List<int>>.value(UTF8.encode(_contents)).asStream();
 
   String toString() {
     // Don't show the whole string if it's long.
     var contents = _contents;
     if (contents.length > 40) {
       contents = contents.substring(0, 20) + " ... " +
                  contents.substring(contents.length - 20);
     }
 
     contents = _escape(contents);
     return 'String "$contents"';
   }
 
   String _escape(String string) {
     return string
         .replaceAll("\"", r'\"')
         .replaceAll("\n", r"\n")
         .replaceAll("\r", r"\r")
         .replaceAll("\t", r"\t");
   }
 }