Remove FilePathWatcher::PlatformDelegate::CancelOnMessageLoopThread().

base/files/file_path_watcher.h

 // 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.
 
 // This module provides a way to monitor a file or directory for changes.
 
 #ifndef BASE_FILES_FILE_PATH_WATCHER_H_
 #define BASE_FILES_FILE_PATH_WATCHER_H_
 
 #include "base/base_export.h"
@@ skipping 35 matching lines @@
     // allow to shut down properly while the object is still alive.
     // It can be called from any thread.
     virtual void Cancel() = 0;
 
    protected:
     friend class base::RefCountedThreadSafe<PlatformDelegate>;
     friend class FilePathWatcher;
 
     virtual ~PlatformDelegate();
 
-    // Stop watching. This is only called on the thread of the appropriate
-    // message loop. Since it can also be called more than once, it should
-    // check |is_cancelled()| to avoid duplicate work.
-    virtual void CancelOnMessageLoopThread() = 0;
-
     scoped_refptr<base::SingleThreadTaskRunner> task_runner() const {
       return task_runner_;
     }
 
     void set_task_runner(scoped_refptr<base::SingleThreadTaskRunner> runner) {
       task_runner_ = std::move(runner);
     }
 
     // Must be called before the PlatformDelegate is deleted.
     void set_cancelled() {
@@ skipping 31 matching lines @@
 
  private:
   scoped_refptr<PlatformDelegate> impl_;
 
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_PATH_WATCHER_H_