Use FSEvents for recursive file watch on Mac

base/files/file_path_watcher_linux.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/files/file_path_watcher.h"
 
 #include <errno.h>
 #include <string.h>
 #include <sys/inotify.h>
 #include <sys/ioctl.h>
@@ skipping 445 matching lines @@
   if (!message_loop()->BelongsToCurrentThread()) {
     message_loop()->PostTask(FROM_HERE,
                              Bind(&FilePathWatcher::CancelWatch,
                                   make_scoped_refptr(this)));
   } else {
     CancelOnMessageLoopThread();
   }
 }
 
 void FilePathWatcherImpl::CancelOnMessageLoopThread() {
+  DCHECK(message_loop()->BelongsToCurrentThread());
   set_cancelled();
 
   if (!callback_.is_null()) {
     MessageLoop::current()->RemoveDestructionObserver(this);
     callback_.Reset();
   }
 
   for (size_t i = 0; i < watches_.size(); ++i)
     g_inotify_reader.Get().RemoveWatch(watches_[i].watch, this);
   watches_.clear();
@@ skipping 183 matching lines @@
   return watches_[watches_.size() - 1].subdir.empty();
 }
 
 }  // namespace
 
 FilePathWatcher::FilePathWatcher() {
   impl_ = new FilePathWatcherImpl();
 }
 
 }  // namespace base