Use metadata annotation @patch for patch classes

runtime/lib/print_patch.dart

 // Copyright (c) 2012, 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.
 
 // A print-closure gets a String that should be printed. In general the
 // string is a line, but it may contain "\n" characters.
 typedef void _PrintClosure(String line);
 
-patch void printToConsole(String line) {
+@patch void printToConsole(String line) {
   _printClosure(line);
 }
 
 void _unsupportedPrint(String line) {
   throw new UnsupportedError("'print' is not supported");
 }
 
 // _printClosure can be overwritten by the embedder to supply a different
 // print implementation.
 _PrintClosure _printClosure = _unsupportedPrint;