add @MirrorsUsed to observe/polymer/polymer_exprs pkgs

pkg/polymer_expressions/test/syntax_test.dart

Index: pkg/polymer_expressions/test/syntax_test.dart
diff --git a/pkg/polymer_expressions/test/syntax_test.dart b/pkg/polymer_expressions/test/syntax_test.dart
index 32b5f63262cdeae841d547a020969d43d4e2b6fe..ceb13077a03413d55e16af0cf10b8490a53c208e 100644
--- a/pkg/polymer_expressions/test/syntax_test.dart
+++ b/pkg/polymer_expressions/test/syntax_test.dart
@@ -82,6 +82,7 @@ main() {
   });
 }
 
+@reflectable
 class Person extends ChangeNotifierBase {
   String _firstName;
   String _lastName;
@@ -92,15 +93,13 @@ class Person extends ChangeNotifierBase {
   String get firstName => _firstName;
 
   void set firstName(String value) {
-    _firstName = value;
-    notifyChange(new PropertyChangeRecord(#firstName));
+    _firstName = notifyPropertyChange(#firstName, _firstName, value);
   }
 
   String get lastName => _lastName;
 
   void set lastName(String value) {
-    _lastName = value;
-    notifyChange(new PropertyChangeRecord(#lastName));
+    _lastName = notifyPropertyChange(#lastName, _lastName, value);
   }
 
   String getFullName() => '$_firstName $_lastName';
@@ -108,10 +107,8 @@ class Person extends ChangeNotifierBase {
   List<String> get items => _items;
 
   void set items(List<String> value) {
-    _items = value;
-    notifyChange(new PropertyChangeRecord(#items));
+    _items = notifyPropertyChange(#items, _items, value);
   }
 
   String toString() => "Person(firstName: $_firstName, lastName: $_lastName)";
-
 }