Remove Encoding-enum from dart:io and add interface in dart:convert.

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: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].
@@ skipping 12 matching lines @@
   factory Asset.fromString(AssetId id, String content) =>
       new _StringAsset(id, content);
 
   factory Asset.fromPath(AssetId id, String path) =>
       new _FileAsset(id, new File(path));
 
   /// Returns the contents of the asset as a string.
   ///
   /// If the asset was created from a [String] the original string is always
   /// returned and [encoding] is ignored. Otherwise, the binary data of the
-  /// asset is decoded using [encoding], which defaults to [Encoding.UTF_8].
+  /// asset is decoded using [encoding], which defaults to [UTF8].
   Future<String> readAsString({Encoding encoding});
 
   /// Streams the binary contents of the asset.
   ///
   /// If the asset was created from a [String], this returns its UTF-8 encoding.
   Stream<List<int>> read();
 }
 
 /// An asset whose data is stored in a list of bytes.
 class _BinaryAsset extends Asset {
   final List<int> _contents;
 
   _BinaryAsset(AssetId id, this._contents)
       : super(id);
 
   Future<String> readAsString({Encoding encoding}) {
-    if (encoding == null) encoding = Encoding.UTF_8;
+    if (encoding == null) encoding = UTF8;
 
-    // TODO(rnystrom): When #6284 is fixed, just use that. Until then, only
-    // UTF-8 is supported. :(
-    if (encoding != Encoding.UTF_8) {
-      throw new UnsupportedError(
-          "${encoding.name} is not a supported encoding.");
-    }
-
-    return new Future.value(decodeUtf8(_contents));
+    return new Future.value(encoding.decode(_contents));
   }
 
   Stream<List<int>> read() => new Future<List<int>>.value(_contents).asStream();
 
   String toString() {
     var buffer = new StringBuffer();
     buffer.write("Bytes [");
 
     // Don't show the whole list if it's long.
     if (_contents.length > 11) {
@@ skipping 20 matching lines @@
   }
 }
 
 /// An asset backed by a file on the local file system.
 class _FileAsset extends Asset {
   final File _file;
   _FileAsset(AssetId id, this._file)
       : super(id);
 
   Future<String> readAsString({Encoding encoding}) {
-    if (encoding == null) encoding = Encoding.UTF_8;
+    if (encoding == null) encoding = UTF8;
     return _file.readAsString(encoding: encoding);
   }
 
   Stream<List<int>> read() => _file.openRead();
 
   String toString() => 'File "${_file.path}"';
 }
 
 /// An asset whose data is stored in a string.
 class _StringAsset extends Asset {
@@ skipping 21 matching lines @@
   }
 
   String _escape(String string) {
     return string
         .replaceAll("\"", r'\"')
         .replaceAll("\n", r"\n")
         .replaceAll("\r", r"\r")
         .replaceAll("\t", r"\t");
   }
 }