Changes in polymer-expressions to prepare for codegen in polymer:

pkg/polymer_expressions/test/visitor_test.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 visitor_test;
 
 import 'package:polymer_expressions/parser.dart';
 import 'package:polymer_expressions/visitor.dart';
 import 'package:unittest/unittest.dart';
 
 main() {
 
   group('visitor', () {
 
     // regression test
     test('should not infinitely recurse on parenthesized expressions', () {
       var visitor = new TestVisitor();
       var expr = new Parser('(1)').parse();
       visitor.visit(expr);
     });
 
   });
 }
 
-class TestVisitor extends RecursiveVisitor {
-  visitExpression(e) => null;
-}
+class TestVisitor extends RecursiveVisitor {}