Properly fix DirWatcherTest.SubDir on Vista.

base/directory_watcher.h

Index: base/directory_watcher.h
===================================================================
--- base/directory_watcher.h	(revision 6529)
+++ base/directory_watcher.h	(working copy)
@@ -14,8 +14,10 @@
 class FilePath;
 
 // This class lets you register interest in changes on a directory.
-// The delegate will get called whenever a file is added or changed in the
-// directory.
+// The delegate will get called whenever a file is added, deleted,
+// renamed or modified in the directory, and also when a directory
+// is created, deleted or renamed in the directory. Does not watch
+// subdirectories.
 class DirectoryWatcher {
  public:
   class Delegate {