Use metadata annotation @patch for patch classes

runtime/bin/stdio_patch.dart

Index: runtime/bin/stdio_patch.dart
diff --git a/runtime/bin/stdio_patch.dart b/runtime/bin/stdio_patch.dart
index cf0281991d93ee43c47e554fdfb6b077e7295b83..3c258c56d304a29184aeb32400d293da0c79eb76 100644
--- a/runtime/bin/stdio_patch.dart
+++ b/runtime/bin/stdio_patch.dart
@@ -2,7 +2,7 @@
 // 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 _StdIOUtils {
+@patch class _StdIOUtils {
   static Stdin _getStdioInputStream() {
     switch (_getStdioHandleType(0)) {
       case _STDIO_HANDLE_TYPE_TERMINAL:
@@ -46,14 +46,14 @@ patch class _StdIOUtils {
   static _getStdioHandleType(int fd) native "File_GetStdioHandleType";
 }
 
-patch class Stdin {
-  /* patch */ int readByteSync() native "Stdin_ReadByte";
+@patch class Stdin {
+  /* @patch */ int readByteSync() native "Stdin_ReadByte";
 
-  /* patch */ bool get echoMode => _echoMode;
-  /* patch */ void set echoMode(bool enabled) { _echoMode = enabled; }
+  /* @patch */ bool get echoMode => _echoMode;
+  /* @patch */ void set echoMode(bool enabled) { _echoMode = enabled; }
 
-  /* patch */ bool get lineMode => _lineMode;
-  /* patch */ void set lineMode(bool enabled) { _lineMode = enabled; }
+  /* @patch */ bool get lineMode => _lineMode;
+  /* @patch */ void set lineMode(bool enabled) { _lineMode = enabled; }
 
   static bool get _echoMode native "Stdin_GetEchoMode";
   static void set _echoMode(bool enabled) native "Stdin_SetEchoMode";
@@ -61,8 +61,8 @@ patch class Stdin {
   static void set _lineMode(bool enabled) native "Stdin_SetLineMode";
 }
 
-patch class Stdout {
-  /* patch */ bool _hasTerminal(int fd) {
+@patch class Stdout {
+  /* @patch */ bool _hasTerminal(int fd) {
     try {
       _terminalSize(fd);
       return true;
@@ -71,8 +71,8 @@ patch class Stdout {
     }
   }
 
-  /* patch */ int _terminalColumns(int fd) => _terminalSize(fd)[0];
-  /* patch */ int _terminalLines(int fd) => _terminalSize(fd)[1];
+  /* @patch */ int _terminalColumns(int fd) => _terminalSize(fd)[0];
+  /* @patch */ int _terminalLines(int fd) => _terminalSize(fd)[1];
 
   static List _terminalSize(int fd) {
     var size = _getTerminalSize(fd);