Use metadata annotation @patch for patch classes

runtime/lib/identical_patch.dart

Index: runtime/lib/identical_patch.dart
diff --git a/runtime/lib/identical_patch.dart b/runtime/lib/identical_patch.dart
index 172478f57c4106be1294a9d131d02b76f0f119e6..6aaa1fc0a5382e7d0089fb646af216597f7cbcca 100644
--- a/runtime/lib/identical_patch.dart
+++ b/runtime/lib/identical_patch.dart
@@ -2,6 +2,6 @@
 // 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 bool identical(Object a, Object b) native "Identical_comparison";
+@patch bool identical(Object a, Object b) native "Identical_comparison";
 
-patch int identityHashCode(Object object) => object._identityHashCode;
+@patch int identityHashCode(Object object) => object._identityHashCode;