Add null literals to polymer expressions

pkg/polymer_expressions/test/parser_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 parser_test;
 
 import 'package:polymer_expressions/parser.dart';
 import 'package:polymer_expressions/expression.dart';
 import 'package:unittest/unittest.dart';
 
 expectParse(String s, Expression e) =>
     expect(new Parser(s).parse(), e, reason: s);
 
 main() {
 
   group('parser', () {
 
     test('should parse an empty expression', () {
       expectParse('', empty());
     });
 
     test('should parse an identifier', () {
       expectParse('abc', ident('abc'));
     });
 
     test('should parse a string literal', () {
       expectParse('"abc"', literal('abc'));
     });
 
+    test('should parse a bool literal', () {
+      expectParse('true', literal(true));
+      expectParse('false', literal(false));
+    });
+
+    test('should parse a null literal', () {
+      expectParse('null', literal(null));
+    });
+
     test('should parse an integer literal', () {
       expectParse('123', literal(123));
     });
 
     test('should parse a double literal', () {
       expectParse('1.23', literal(1.23));
     });
 
     test('should parse a positive double literal', () {
       expectParse('+1.23', literal(1.23));
@@ skipping 150 matching lines @@
               literal('a'), invoke(ident('foo'), null, [literal('a')]))]));
     });
 
     test('should parse map literals with method calls', () {
       expectParse("{'a': 1}.length",
           invoke(mapLiteral([mapLiteralEntry(literal('a'), literal(1))]),
               'length'));
     });
   });
 }