Remove FilePathWatcher::PlatformDelegate::CancelOnMessageLoopThread().

base/files/file_path_watcher_mac.cc

 // Copyright 2014 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 "base/files/file_path_watcher_kqueue.h"
 #include "build/build_config.h"
 
 #if !defined(OS_IOS)
 #include "base/files/file_path_watcher_fsevents.h"
@@ skipping 22 matching lines @@
     DCHECK(impl_.get());
     return impl_->Watch(path, recursive, callback);
   }
 
   void Cancel() override {
     if (impl_.get())
       impl_->Cancel();
     set_cancelled();
   }
 
-  void CancelOnMessageLoopThread() override {
-    if (impl_.get())
-      impl_->Cancel();
-    set_cancelled();
-  }
-
  protected:
   ~FilePathWatcherImpl() override {}
 
   scoped_refptr<PlatformDelegate> impl_;
 };
 
 }  // namespace
 
 FilePathWatcher::FilePathWatcher() {
   impl_ = new FilePathWatcherImpl();
 }
 
 }  // namespace base