Implement @patch annotation for patch class members

runtime/lib/core_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.
 
 import "dart:math";
 import "dart:typed_data";
 
 // Equivalent of calling FATAL from C++ code.
 _fatal(msg) native "DartCore_fatal";
 
@@ skipping 58 matching lines @@
         yieldEachIterator = (_current as Iterable).iterator;
         _current = null;
         continue;
       }
       return true;
     }
   }
 }
 
 @patch class StackTrace {
-  /* @patch */ static StackTrace get current native "StackTrace_current";
+  @patch static StackTrace get current native "StackTrace_current";
 }