- Apply review comments from https://codereview.chromium.org/232223004/

sdk/lib/io/file_system_entity.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 /**
  * The type of an entity on the file system, such as a file, directory, or link.
  *
  * These constants are used by the [FileSystemEntity] class
@@ skipping 641 matching lines @@
     if (result is OSError) {
       throw new FileSystemException(msg, path, result);
     } else if (result is ArgumentError) {
       throw result;
     }
   }
 
   static String _trimTrailingPathSeparators(String path) {
     // Don't handle argument errors here.
     if (path is! String) return path;
-    if (Platform.operatingSystem == 'windows') {
+    if (Platform.isWindows) {
       while (path.length > 1 &&
              (path.endsWith(Platform.pathSeparator) ||
               path.endsWith('/'))) {
         path = path.substring(0, path.length - 1);
       }
     } else {
       while (path.length > 1 && path.endsWith(Platform.pathSeparator)) {
         path = path.substring(0, path.length - 1);
       }
     }
     return path;
   }
 
   static String _ensureTrailingPathSeparators(String path) {
     // Don't handle argument errors here.
     if (path is! String) return path;
     if (path.isEmpty) path = '.';
-    if (Platform.operatingSystem == 'windows') {
+    if (Platform.isWindows) {
       while (!path.endsWith(Platform.pathSeparator) && !path.endsWith('/')) {
         path = "$path${Platform.pathSeparator}";
       }
     } else {
       while (!path.endsWith(Platform.pathSeparator)) {
         path = "$path${Platform.pathSeparator}";
       }
     }
     return path;
   }
@@ skipping 115 matching lines @@
     return buffer.toString();
   }
 }
 
 
 class _FileSystemWatcher {
   external static Stream<FileSystemEvent> watch(
       String path, int events, bool recursive);
   external static bool get isSupported;
 }