Use metadata annotation @patch for patch classes

runtime/bin/filter_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.
 
 
 class _FilterImpl extends NativeFieldWrapperClass1 implements _Filter {
   void process(List<int> data, int start, int end) native "Filter_Process";
 
   List<int> processed({bool flush: true, bool end: false})
       native "Filter_Processed";
@@ skipping 10 matching lines @@
 class _ZLibDeflateFilter extends _FilterImpl {
   _ZLibDeflateFilter(bool gzip, int level, int windowBits, int memLevel,
                      int strategy, List<int> dictionary, bool raw) {
     _init(gzip, level, windowBits, memLevel, strategy, dictionary, raw);
   }
   void _init(bool gzip, int level, int windowBits, int memLevel,
              int strategy, List<int> dictionary, bool raw)
       native "Filter_CreateZLibDeflate";
 }
 
-patch class _Filter {
-  /* patch */ static _Filter _newZLibDeflateFilter(bool gzip, int level,
-                                                   int windowBits, int memLevel,
-                                                   int strategy,
-                                                   List<int> dictionary,
-                                                   bool raw) =>
+@patch class _Filter {
+  /* @patch */ static _Filter _newZLibDeflateFilter(bool gzip, int level,
+                                                    int windowBits, int memLevel,
+                                                    int strategy,
+                                                    List<int> dictionary,
+                                                    bool raw) =>
       new _ZLibDeflateFilter(gzip, level, windowBits, memLevel, strategy,
                              dictionary, raw);
-  /* patch */ static _Filter _newZLibInflateFilter(int windowBits,
-                                                   List<int> dictionary,
-                                                   bool raw) =>
+  /* @patch */ static _Filter _newZLibInflateFilter(int windowBits,
+                                                    List<int> dictionary,
+                                                    bool raw) =>
       new _ZLibInflateFilter(windowBits, dictionary, raw);
 }