Fix warnings and hints.

pkg/utf/lib/utf_stream.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.
 
-part of dart.utf;
+part of utf;
 
 abstract class _StringDecoder
     extends StreamEventTransformer<List<int>, String> {
   List<int> _carry;
   List<int> _buffer;
   int _replacementChar;
 
   _StringDecoder(int this._replacementChar);
 
   void handleData(List<int> bytes, EventSink<String> sink) {
@@ skipping 173 matching lines @@
       }
       for (int i = additionalBytes; i > 0; i--) {
         // 10xxxxxx (xxxxxx is next 6 bits from the top).
         bytes.add(((charCode >> (6 * (i - 1))) & 0x3F) | 0x80);
       }
       pos += additionalBytes + 1;
     }
     return bytes;
   }
 }