use symbol literals instead of const ctor in packages

pkg/mdv/test/node_bindings_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 node_bindings_test;
 
 import 'dart:html';
 import 'package:mdv/mdv.dart' as mdv;
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
 import 'mdv_test_utils.dart';
 
 // Note: this file ported from
 // https://github.com/toolkitchen/mdv/blob/master/tests/node_bindings.js
 
 main() {
   mdv.initialize();
   useHtmlConfiguration();
   group('Node Bindings', nodeBindingTests);
 }
 
-sym(x) => new Symbol(x);
-
 nodeBindingTests() {
   var testDiv;
 
   setUp(() {
     document.body.append(testDiv = new DivElement());
   });
 
   tearDown(() {
     testDiv.remove();
     testDiv = null;
   });
 
   observeTest('Text', () {
     var text = new Text('hi');
     var model = toSymbolMap({'a': 1});
     text.bind('text', model, 'a');
     expect(text.text, '1');
 
-    model[sym('a')] = 2;
+    model[#a] = 2;
     performMicrotaskCheckpoint();
     expect(text.text, '2');
 
     text.unbind('text');
-    model[sym('a')] = 3;
+    model[#a] = 3;
     performMicrotaskCheckpoint();
     expect(text.text, '2');
 
     // TODO(rafaelw): Throw on binding to unavailable property?
   });
 
   observeTest('Element', () {
     var element = new DivElement();
     var model = toSymbolMap({'a': 1, 'b': 2});
     element.bind('hidden?', model, 'a');
     element.bind('id', model, 'b');
 
     expect(element.attributes, contains('hidden'));
     expect(element.attributes['hidden'], '');
     expect(element.id, '2');
 
-    model[sym('a')] = null;
+    model[#a] = null;
     performMicrotaskCheckpoint();
     expect(element.attributes, isNot(contains('hidden')),
         reason: 'null is false-y');
 
-    model[sym('a')] = false;
+    model[#a] = false;
     performMicrotaskCheckpoint();
     expect(element.attributes, isNot(contains('hidden')));
 
-    model[sym('a')] = 'foo';
-    model[sym('b')] = 'x';
+    model[#a] = 'foo';
+    model[#b] = 'x';
     performMicrotaskCheckpoint();
     expect(element.attributes, contains('hidden'));
     expect(element.attributes['hidden'], '');
     expect(element.id, 'x');
   });
 
   inputTextAreaValueTest(String tagName) {
     var el = new Element.tag(tagName);
     testDiv.nodes.add(el);
     var model = toSymbolMap({'x': 42});
     el.bind('value', model, 'x');
     expect(el.value, '42');
 
-    model[sym('x')] = 'Hi';
+    model[#x] = 'Hi';
     expect(el.value, '42', reason: 'changes delivered async');
     performMicrotaskCheckpoint();
     expect(el.value, 'Hi');
 
     el.value = 'changed';
     dispatchEvent('input', el);
-    expect(model[sym('x')], 'changed');
+    expect(model[#x], 'changed');
 
     el.unbind('value');
 
     el.value = 'changed again';
     dispatchEvent('input', el);
-    expect(model[sym('x')], 'changed');
+    expect(model[#x], 'changed');
 
     el.bind('value', model, 'x');
-    model[sym('x')] = null;
+    model[#x] = null;
     performMicrotaskCheckpoint();
     expect(el.value, '');
   }
 
   observeTest('Input.value', () => inputTextAreaValueTest('input'));
   observeTest('TextArea.value', () => inputTextAreaValueTest('textarea'));
 
   observeTest('Radio Input', () {
     var input = new InputElement();
     input.type = 'radio';
     var model = toSymbolMap({'x': true});
     input.bind('checked', model, 'x');
     expect(input.checked, true);
 
-    model[sym('x')] = false;
+    model[#x] = false;
     expect(input.checked, true);
     performMicrotaskCheckpoint();
     expect(input.checked, false,reason: 'model change should update checked');
 
     input.checked = true;
     dispatchEvent('change', input);
-    expect(model[sym('x')], true, reason: 'input.checked should set model');
+    expect(model[#x], true, reason: 'input.checked should set model');
 
     input.unbind('checked');
 
     input.checked = false;
     dispatchEvent('change', input);
-    expect(model[sym('x')], true,
+    expect(model[#x], true,
         reason: 'disconnected binding should not fire');
   });
 
   observeTest('Checkbox Input', () {
     var input = new InputElement();
     testDiv.append(input);
     input.type = 'checkbox';
     var model = toSymbolMap({'x': true});
     input.bind('checked', model, 'x');
     expect(input.checked, true);
 
-    model[sym('x')] = false;
+    model[#x] = false;
     expect(input.checked, true, reason: 'changes delivered async');
     performMicrotaskCheckpoint();
     expect(input.checked, false);
 
     input.click();
-    expect(model[sym('x')], true);
+    expect(model[#x], true);
     performMicrotaskCheckpoint();
 
     input.click();
-    expect(model[sym('x')], false);
+    expect(model[#x], false);
   });
 }