Some more removals of dart:utf.

sdk/lib/_internal/compiler/implementation/source_file_provider.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 source_file_provider;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
-import 'dart:utf';
 
 import '../compiler.dart' as api show Diagnostic;
 import 'dart2js.dart' show AbortLeg;
 import 'colors.dart' as colors;
 import 'source_file.dart';
 import 'filenames.dart';
 import 'util/uri_extras.dart';
 
 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(buffer);
 }
 
 class SourceFileProvider {
   bool isWindows = (Platform.operatingSystem == 'windows');
   Uri cwd = currentDirectory;
   Map<String, SourceFile> sourceFiles = <String, SourceFile>{};
   int dartCharactersRead = 0;
 
   Future<String> readStringFromUri(Uri resourceUri) {
     if (resourceUri.scheme != 'file') {
@@ skipping 96 matching lines @@
     if (fatal && throwOnError) {
       isAborting = true;
       throw new AbortLeg(message);
     }
   }
 
   void call(Uri uri, int begin, int end, String message, api.Diagnostic kind) {
     return diagnosticHandler(uri, begin, end, message, kind);
   }
 }