Use metadata annotation @patch for patch classes

runtime/lib/function_patch.dart

Index: runtime/lib/function_patch.dart
diff --git a/runtime/lib/function_patch.dart b/runtime/lib/function_patch.dart
index c94c78bb902042215d03b10adcb74653a9b3f7f7..7ed74c855a6838e65a4894408b8b52f4c2b87f3f 100644
--- a/runtime/lib/function_patch.dart
+++ b/runtime/lib/function_patch.dart
@@ -2,13 +2,13 @@
 // 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 Function {
+@patch class Function {
   static _apply(List arguments, List names)
       native "Function_apply";
 
-  /* patch */ static apply(Function function,
-                           List positionalArguments,
-                           [Map<Symbol, dynamic> namedArguments]) {
+  /* @patch */ static apply(Function function,
+                            List positionalArguments,
+                            [Map<Symbol, dynamic> namedArguments]) {
     int numPositionalArguments = 1 +  // Function is first implicit argument.
         (positionalArguments != null ? positionalArguments.length : 0);
     int numNamedArguments = namedArguments != null ? namedArguments.length : 0;