Access fields from the appropriate threads in FilePathWatcherFSEvents.

base/files/file_path_watcher_fsevents.h

Index: base/files/file_path_watcher_fsevents.h
diff --git a/base/files/file_path_watcher_fsevents.h b/base/files/file_path_watcher_fsevents.h
index 800c5b43f6879aa0d5d66eb1164f2f69edb3d5a8..da660cb99b99420f3f8200f907484729a9b15683 100644
--- a/base/files/file_path_watcher_fsevents.h
+++ b/base/files/file_path_watcher_fsevents.h
@@ -48,7 +48,9 @@ class FilePathWatcherFSEvents : public FilePathWatcher::PlatformDelegate {
   void DestroyEventStream();
 
   // Start watching the FSEventStream.
-  void StartEventStream(FSEventStreamEventId start_event);
+  void StartEventStream(FSEventStreamEventId start_event,
+                        const FilePath& path,
+                        const FilePathWatcher::Callback& callback);
 
   // Cleans up and stops the event stream.
   void CancelOnMessageLoopThread() override;