Use metadata annotation @patch for patch classes

runtime/lib/regexp_patch.dart

Index: runtime/lib/regexp_patch.dart
diff --git a/runtime/lib/regexp_patch.dart b/runtime/lib/regexp_patch.dart
index d8e622aa7e0f7db3aac22e1f7e4f1d769521f812..9b23430b3e93f30a46cf1dbebc6af2eb4e58f4a1 100644
--- a/runtime/lib/regexp_patch.dart
+++ b/runtime/lib/regexp_patch.dart
@@ -4,10 +4,10 @@
 
 import "dart:collection" show LinkedList, LinkedListEntry;
 
-patch class RegExp {
-  /* patch */ factory RegExp(String source,
-                             {bool multiLine: false,
-                              bool caseSensitive: true}) {
+@patch class RegExp {
+  /* @patch */ factory RegExp(String source,
+                              {bool multiLine: false,
+                               bool caseSensitive: true}) {
     _RegExpHashKey key = new _RegExpHashKey(
         source, multiLine, caseSensitive);
     _RegExpHashValue value = _cache[key];