Use metadata annotation @patch for patch classes

runtime/lib/internal_patch.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // 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 List makeListFixedLength(List growableList)
+@patch List makeListFixedLength(List growableList)
     native "Internal_makeListFixedLength";
 
-patch List makeFixedListUnmodifiable(List fixedLengthList)
+@patch List makeFixedListUnmodifiable(List fixedLengthList)
     native "Internal_makeFixedListUnmodifiable";
 
 class VMLibraryHooks {
   // Example: "dart:isolate _Timer._factory"
   static var timerFactory;
 
   // Example: "dart:io _EventHandler._sendData"
   static var eventHandlerSendData;
 
   // A nullary closure that answers the current clock value in milliseconds.
   // Example: "dart:io _EventHandler._timerMillisecondClock"
   static var timerMillisecondClock;
 
   // Implementation of Resource.readAsBytes.
   static var resourceReadAsBytes;
 
   // Implementation of package root/map provision.
   static var packageRootString;
   static var packageConfigString;
   static var packageRootUriFuture;
   static var packageConfigUriFuture;
   static var resolvePackageUriFuture;
 
   static var platformScript;
 }
 
-patch class CodeUnits {
+@patch class CodeUnits {
   static final int cid = ClassID.getID(new CodeUnits(""));
 }
 
 final bool is64Bit = _inquireIs64Bit();
 
 bool _inquireIs64Bit() native "Internal_inquireIs64Bit";