Changed interfaces to abstract classes in utils.

utils/css/tokenizer_base.dart

 // Copyright (c) 2011, 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.
 // Generated by scripts/tokenizer_gen.py.
 
 
-interface TokenSource {
+abstract class TokenSource {
   Token next();
 }
 
 class InterpStack {
   InterpStack next, previous;
   final int quote;
   final bool isMultiline;
   int depth;
 
   InterpStack(this.previous, this.quote, this.isMultiline): depth = -1;
@@ skipping 427 matching lines @@
     }
     int kind = getIdentifierKind();
     if (kind == TokenKind.IDENTIFIER) {
       return _finishToken(TokenKind.IDENTIFIER);
     } else {
       return _finishToken(kind);
     }
   }
 }