Use metadata annotation @patch for patch classes

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 8a8359ab267e1d4ec40ab0093702de10462531e5..333f62afadf73b8dae2349f052a1aff8bd5adf44 100644
--- a/runtime/lib/map_patch.dart
+++ b/runtime/lib/map_patch.dart
@@ -2,7 +2,7 @@
 // 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.
 
-patch class Map<K, V> {
+@patch class Map<K, V> {
   // Factory constructing a Map from a parser generated Map literal.
   // [elements] contains n key-value pairs.
   // The keys are at position 2*n and are already type checked by the parser
@@ -17,9 +17,9 @@ patch class Map<K, V> {
     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>;
 }