Implement @patch annotation for patch class members

runtime/bin/platform_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.
 
 @patch class _Platform {
-  /* @patch */ static int _numberOfProcessors()
+  @patch static int _numberOfProcessors()
       native "Platform_NumberOfProcessors";
-  /* @patch */ static String _pathSeparator()
+  @patch static String _pathSeparator()
       native "Platform_PathSeparator";
-  /* @patch */ static String _operatingSystem()
+  @patch static String _operatingSystem()
       native "Platform_OperatingSystem";
-  /* @patch */ static _localHostname()
+  @patch static _localHostname()
       native "Platform_LocalHostname";
-  /* @patch */ static _executable()
+  @patch static _executable()
       native "Platform_ExecutableName";
-  /* @patch */ static _resolvedExecutable()
+  @patch static _resolvedExecutable()
       native "Platform_ResolvedExecutableName";
-  /* @patch */ static _environment()
+  @patch static _environment()
       native "Platform_Environment";
-  /* @patch */ static List<String> _executableArguments()
+  @patch static List<String> _executableArguments()
       native "Platform_ExecutableArguments";
-  /* @patch */ static String _version()
+  @patch static String _version()
       native "Platform_GetVersion";
 
-  /* @patch */ static String _packageRoot()
+  @patch static String _packageRoot()
       => VMLibraryHooks.packageRootString;
-  /* @patch */ static String _packageConfig()
+  @patch static String _packageConfig()
       => VMLibraryHooks.packageConfigString;
 
   // This script singleton is written to by the embedder if applicable.
-  /* @patch */ static void set _nativeScript(String path) {
+  @patch static void set _nativeScript(String path) {
     if (path.startsWith('http:') ||
         path.startsWith('https:') ||
         path.startsWith('package:') ||
         path.startsWith('dart:') ||
         path.startsWith('data:') ||
         path.startsWith('file:')) {
       script = Uri.parse(path);
     } else {
       script = Uri.base.resolveUri(new Uri.file(path));
     }
     VMLibraryHooks.platformScript = script;
   }
 }