dart:platform | Remove isWindows, isLinux, isAndroid, isMacOS from dart:platform.

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 295 matching lines @@
 }
 
 
 String _filePathFromHttpUri(Uri uri) {
   _logResolution('# Path: $uri -> $uri');
   return uri.toString();
 }
 
 
 class _PlatformHook {
+  // TODO(whesse):  Replace uses of Platform with uses of internal _Platform
+  //   class, to prepare for removal of (deprecated) Platform class.
+  //   Also merge _Platform and _PlatformHook class into _Platform class
+  //   at that time, since _PlatformHook is the only user of _Platform.
   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;
   Uri get script => new Uri.file(Platform.script);
   String get executable => Platform.executable;
   List<String>  get executableArguments => Platform.executableArguments;
   String get packageRoot => Platform.packageRoot;
 }
 
 
 _getPlatform() => new _PlatformHook();