Changed interfaces to abstract classes in utils.

utils/peg/pegparser.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.
 
 #library('Peg Parser');
 
 /*
  * The following functions are combinators for building Rules.
  *
  * A rule is one of the following
@@ skipping 319 matching lines @@
   // Used for constructing an error message.
   int inhibitExpectedTrackingDepth = 0;
   int max_pos = 0;
   var max_rule;
 }
 
 /**
  * An interface tag for rules. If this tag is on a rule, then the description()
  * of the rule is something sensible to put in a message.
  */
-interface _Expectable {
+abstract class _Expectable {
   String description();
 }
 
 class _Rule {
   const _Rule();
   // Returns null for a match failure or [pos, ast] for success.
   match(_ParserState state, int pos) {
     if (! state.inWhitespaceMode) {
       pos = _skip_whitespace(state, pos);
     }
@@ skipping 498 matching lines @@
   add(s);
   add(t);
   add(u);
   add(v);
   add(w);
   add(x);
   add(y);
   add(z);
   return list;
 }