Add fields to platform library, implement them on runtime dart.

runtime/bin/builtin.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.
 
 library builtin;
 import 'dart:io';
 
 // Corelib 'print' implementation.
 void _print(arg) {
   _Logger._printString(arg.toString());
@@ skipping 292 matching lines @@
   }
   _logResolution('# Package: $uri -> $path');
   return path;
 }
 
 
 String _filePathFromHttpUri(Uri uri) {
   _logResolution('# Path: $uri -> $uri');
   return uri.toString();
 }
+
+
+class _PlatformHook {
+  int get numberOfProcessors => Platform.numberOfProcessors;
+  String get pathSeparator => Platform.pathSeparator;
+  String get operatingSystem => Platform.operatingSystem;
+  String get localHostname => Platform.localHostname;
+  String get version => Platform.version;
+  Map<String, String> get environment => Platform.environment;
+  String get script => Platform.script;
+  String get executable => Platform.executable;
+  List<String>  get executableArguments => Platform.executableArguments;
+  String get packageRoot => Platform.packageRoot;
+}
+
+
+_getPlatform() => new _PlatformHook();
+
+
+