use symbol literals instead of const ctor in packages

pkg/observe/test/path_observer_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.
 
 import 'package:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 import 'observe_test_utils.dart';
 
 // This file contains code ported from:
 // https://github.com/rafaelw/ChangeSummary/blob/master/tests/test.js
 
 main() {
   group('PathObserver', observePathTests);
 }
 
 observePath(obj, path) => new PathObserver(obj, path);
 
-sym(x) => new Symbol(x);
-
 toSymbolMap(Map map) {
   var result = new ObservableMap.linked();
   map.forEach((key, value) {
     if (value is Map) value = toSymbolMap(value);
     result[new Symbol(key)] = value;
   });
   return result;
 }
 
 observePathTests() {
@@ skipping 34 matching lines @@
     obj.value = new ObservableBox(4);
     expect(observePath(obj, 'value.value.value').value, null);
     expect(observePath(obj, 'value.value').value, 4);
   });
 
 
   observeTest('get value at path ObservableMap', () {
     var obj = toSymbolMap({'a': {'b': {'c': 1}}});
 
     expect(observePath(obj, '').value, obj);
-    expect(observePath(obj, 'a').value, obj[sym('a')]);
-    expect(observePath(obj, 'a.b').value, obj[sym('a')][sym('b')]);
+    expect(observePath(obj, 'a').value, obj[#a]);
+    expect(observePath(obj, 'a.b').value, obj[#a][#b]);
     expect(observePath(obj, 'a.b.c').value, 1);
 
-    obj[sym('a')][sym('b')][sym('c')] = 2;
+    obj[#a][#b][#c] = 2;
     expect(observePath(obj, 'a.b.c').value, 2);
 
-    obj[sym('a')][sym('b')] = toSymbolMap({'c': 3});
+    obj[#a][#b] = toSymbolMap({'c': 3});
     expect(observePath(obj, 'a.b.c').value, 3);
 
-    obj[sym('a')] = toSymbolMap({'b': 4});
+    obj[#a] = toSymbolMap({'b': 4});
     expect(observePath(obj, 'a.b.c').value, null);
     expect(observePath(obj, 'a.b').value, 4);
   });
 
   observeTest('set value at path', () {
     var obj = toSymbolMap({});
     observePath(obj, 'foo').value = 3;
-    expect(obj[sym('foo')], 3);
+    expect(obj[#foo], 3);
 
     var bar = toSymbolMap({ 'baz': 3 });
     observePath(obj, 'bar').value = bar;
-    expect(obj[sym('bar')], bar);
+    expect(obj[#bar], bar);
 
     observePath(obj, 'bar.baz.bat').value = 'not here';
     expect(observePath(obj, 'bar.baz.bat').value, null);
   });
 
   observeTest('set value back to same', () {
     var obj = toSymbolMap({});
     var path = observePath(obj, 'foo');
     var values = [];
     path.changes.listen((_) { values.add(path.value); });
 
     path.value = 3;
-    expect(obj[sym('foo')], 3);
+    expect(obj[#foo], 3);
     expect(path.value, 3);
 
     observePath(obj, 'foo').value = 2;
     performMicrotaskCheckpoint();
     expect(path.value, 2);
     expect(observePath(obj, 'foo').value, 2);
 
     observePath(obj, 'foo').value = 3;
     performMicrotaskCheckpoint();
     expect(path.value, 3);
 
     performMicrotaskCheckpoint();
     expect(values, [2, 3]);
   });
 
   observeTest('Observe and Unobserve - Paths', () {
     var arr = toSymbolMap({});
 
-    arr[sym('foo')] = 'bar';
+    arr[#foo] = 'bar';
     var fooValues = [];
     var fooPath = observePath(arr, 'foo');
     var fooSub = fooPath.changes.listen((_) {
       fooValues.add(fooPath.value);
     });
-    arr[sym('foo')] = 'baz';
-    arr[sym('bat')] = 'bag';
+    arr[#foo] = 'baz';
+    arr[#bat] = 'bag';
     var batValues = [];
     var batPath = observePath(arr, 'bat');
     var batSub = batPath.changes.listen((_) {
       batValues.add(batPath.value);
     });
 
     performMicrotaskCheckpoint();
     expect(fooValues, ['baz']);
     expect(batValues, []);
 
-    arr[sym('foo')] = 'bar';
+    arr[#foo] = 'bar';
     fooSub.cancel();
-    arr[sym('bat')] = 'boo';
+    arr[#bat] = 'boo';
     batSub.cancel();
-    arr[sym('bat')] = 'boot';
+    arr[#bat] = 'boot';
 
     performMicrotaskCheckpoint();
     expect(fooValues, ['baz']);
     expect(batValues, []);
   });
 
   observeTest('Path Value With Indices', () {
     var model = toObservable([]);
     var path = observePath(model, '0');
     path.changes.listen(expectAsync1((_) {
@@ skipping 47 matching lines @@
   }
 
   observeTest('observe map', () {
     var model = toSymbolMap({'a': 1});
     var path = observePath(model, 'a');
 
     var values = [path.value];
     var sub = path.changes.listen((_) { values.add(path.value); });
     expect(values, [1]);
 
-    model[sym('a')] = 2;
+    model[#a] = 2;
     performMicrotaskCheckpoint();
     expect(values, [1, 2]);
 
     sub.cancel();
-    model[sym('a')] = 3;
+    model[#a] = 3;
     performMicrotaskCheckpoint();
     expect(values, [1, 2]);
   });
 }
 
 class TestModel extends ChangeNotifierBase {
   var _a, _b, _c;
 
   TestModel();
 
   get a => _a;
 
   void set a(newValue) {
-    _a = notifyPropertyChange(const Symbol('a'), _a, newValue);
+    _a = notifyPropertyChange(#a, _a, newValue);
   }
 
   get b => _b;
 
   void set b(newValue) {
-    _b = notifyPropertyChange(const Symbol('b'), _b, newValue);
+    _b = notifyPropertyChange(#b, _b, newValue);
   }
 
   get c => _c;
 
   void set c(newValue) {
-    _c = notifyPropertyChange(const Symbol('c'), _c, newValue);
+    _c = notifyPropertyChange(#c, _c, newValue);
   }
 }
 
 class WatcherModel extends ObservableBase {
   // TODO(jmesserly): dart2js does not let these be on the same line:
   // @observable var a, b, c;
   @observable var a;
   @observable var b;
   @observable var c;
 
   WatcherModel();
 }