Implement @patch annotation for patch class members

runtime/lib/map_patch.dart

Index: runtime/lib/map_patch.dart
diff --git a/runtime/lib/map_patch.dart b/runtime/lib/map_patch.dart
index 333f62afadf73b8dae2349f052a1aff8bd5adf44..6e2f14df885046668c27ac437d5d251e642ef9b9 100644
--- a/runtime/lib/map_patch.dart
+++ b/runtime/lib/map_patch.dart
@@ -17,9 +17,9 @@
     return map;
   }
 
-  /* @patch */ factory Map.unmodifiable(Map other) {
+  @patch factory Map.unmodifiable(Map other) {
     return new UnmodifiableMapView<K, V>(new Map.from(other));
   }
 
-  /* @patch */ factory Map() = LinkedHashMap<K, V>;
+  @patch factory Map() = LinkedHashMap<K, V>;
 }