Make file system watcher compile on Mac OS 106, and add a runtime-call to test if the system suppor…

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;
 
 class FileSystemEntityType {
   static const FILE = const FileSystemEntityType._internal(0);
   static const DIRECTORY = const FileSystemEntityType._internal(1);
   static const LINK = const FileSystemEntityType._internal(2);
@@ skipping 326 matching lines @@
    * being listened to, not when the call to [watch] is issued. Note that the
    * returned [Stream] is endless. To stop the [Stream], simply cancel the
    * subscription.
    */
   Stream<FileSystemEvent> watch({int events: FileSystemEvent.ALL,
                                  bool recursive: false})
      => new _FileSystemWatcher(_trimTrailingPathSeparators(path),
                                events,
                                recursive).stream;
 
+  /**
+   * Test if [watch] is supported on the current system.
+   *
+   * Mac OS 10.6 and below is not supported.
+   */
+  static bool get isWatchSupported => _FileSystemWatcher.isSupported;
+
 
   /**
    * Finds the type of file system object that a path points to. Returns
    * a [:Future<FileSystemEntityType>:] that completes with the result.
    *
    * [FileSystemEntityType] has the constant instances FILE, DIRECTORY,
    * LINK, and NOT_FOUND.  [type] will return LINK only if the optional
    * named argument [followLinks] is false, and [path] points to a link.
    * If the path does not point to a file system object, or any other error
    * occurs in looking up the path, NOT_FOUND is returned.  The only
@@ skipping 173 matching lines @@
     buffer.write("FileSystemMoveEvent('$path'");
     if (destination != null) buffer.write(", '$destination'");
     buffer.write(')');
     return buffer.toString();
   }
 }
 
 
 abstract class _FileSystemWatcher {
   external factory _FileSystemWatcher(String path, int events, bool recursive);
+  external static bool get isSupported;
 
   Stream<FileSystemEvent> get stream;
 }