refactor(dart/transform tests): Use actual directive def'n instead of mock.

In the transformer unit tests, we previously used a mock directive annotation. This update
substitutes the actual Angular2 directive annotations.

Closes #706

modules/angular2/test/transform/simple_annotation_files/bar.dart

@@ -2,7 +2,7 @@ library bar;
 
 import 'package:angular2/src/core/annotations/annotations.dart';
 
-@Directive(context: 'soup')
-class Component {
-  Component();
+@Component(selector: '[soup]')
+class MyComponent {
+  MyComponent();
 }

modules/angular2/test/transform/simple_annotation_files/expected/index.bootstrap.dart

@@ -5,10 +5,10 @@ import 'index.dart' as i2;
 
 main() {
   reflector
-    ..registerType(i0.Component, {
-      "factory": () => new i0.Component(),
+    ..registerType(i0.MyComponent, {
+      "factory": () => new i0.MyComponent(),
       "parameters": const [const []],
-      "annotations": const [const i1.Directive(context: 'soup')]
+      "annotations": const [const i1.Component(selector: '[soup]')]
     });
   i2.main();
 }

modules/angular2/test/transform/simple_annotation_files/index.dart

@@ -3,5 +3,5 @@ library web_foo;
 import 'bar.dart';
 
 void main() {
-  new Component('Things');
+  new MyComponent('Things');
 }