fix list filtering if the filter is a method

pkg/polymer_expressions/test/eval_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 eval_test;
 
 import 'dart:async';
 
 import 'package:polymer_expressions/eval.dart';
 import 'package:polymer_expressions/filter.dart';
@@ skipping 135 matching lines @@
       var topLevel = {
         'a': '42',
         'parseInt': parseInt,
         'add': add,
       };
       expectEval('a | parseInt()', 42, null, topLevel);
       expectEval('a | parseInt(8)', 34, null, topLevel);
       expectEval('a | parseInt() | add(10)', 52, null, topLevel);
     });
 
+    test('should filter a list', () {
+      expectEval('chars1 | filteredList', ['a', 'b'], new WordElement());
+    });
+
     test('should return null if the receiver of a method is null', () {
       expectEval('a.b', null, null, {'a': null});
       expectEval('a.b()', null, null, {'a': null});
     });
 
     test('should return null if null is invoked', () {
       expectEval('a()', null, null, {'a': null});
     });
 
     test('should return null if an operand is null', () {
@@ skipping 214 matching lines @@
     expect(value, afterMatcher);
     expect(observer.currentValue, afterMatcher);
     passed = true;
   });
   mutate();
   // fail if we don't receive an update by the next event loop
   return Future.wait([future, new Future(() {
     expect(passed, true, reason: "Didn't receive a change notification on $s");
   })]);
 }
+
+// Regression test from https://code.google.com/p/dart/issues/detail?id=13459
+class WordElement extends ObservableBase {
+  @observable List chars1 = 'abcdefg'.split('');
+  List filteredList(List original) => [original[0], original[1]];
+}