Use FSEvents for recursive file watch on Mac

base/files/file_path_watcher.h

Index: base/files/file_path_watcher.h
diff --git a/base/files/file_path_watcher.h b/base/files/file_path_watcher.h
index 3c1941f012bf5ff620dd3d00edd23256d81c8a3a..b90efa1800fb7eeaa2cfc2d268dc1c09dfd89c4b 100644
--- a/base/files/file_path_watcher.h
+++ b/base/files/file_path_watcher.h
@@ -88,12 +88,15 @@ class BASE_EXPORT FilePathWatcher {
   // shutdown.
   static void CancelWatch(const scoped_refptr<PlatformDelegate>& delegate);
 
+  // Returns true if the platform and OS version support recursive watches.
+  static bool RecursiveWatchAvailable();
+
   // Invokes |callback| whenever updates to |path| are detected. This should be
   // called at most once, and from a MessageLoop of TYPE_IO. Set |recursive| to
   // true, to watch |path| and its children. The callback will be invoked on
   // the same loop. Returns true on success.
   //
-  // NOTE: Recursive watch is not supported on all platforms and file systems.
+  // Recursive watch is not supported on all platforms and file systems.
   // Watch() will return false in the case of failure.
   bool Watch(const FilePath& path, bool recursive, const Callback& callback);