Require FilePathWatcher destructor to be called in sequence with Watch().

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"
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/sequence_checker.h"
 #include "base/single_thread_task_runner.h"
 
 namespace base {
 
 // This class lets you register interest in changes on a FilePath.
 // The callback will get called whenever the file or directory referenced by the
 // FilePath is changed, including created or deleted. Due to limitations in the
 // underlying OS APIs, FilePathWatcher has slightly different semantics on OS X
 // than on Windows or Linux. FilePathWatcher on Linux and Windows will detect
 // modifications to files in a watched directory. FilePathWatcher on Mac will
 // detect the creation and deletion of files in a watched directory, but will
 // not detect modifications to those files. See file_path_watcher_kqueue.cc for
 // details.
+//
+// Must be destructed on the sequence that invokes Watch().

[dcheng, 2016/11/09 18:39:11]

Nit: destroyed is slightly more standard terminology in Chromium

[fdoray, 2016/11/10 15:46:20]

Done.

 class BASE_EXPORT FilePathWatcher {
  public:
   // Callback type for Watch(). |path| points to the file that was updated,
   // and |error| is true if the platform specific code detected an error. In
   // that case, the callback won't be invoked again.
   typedef base::Callback<void(const FilePath& path, bool error)> Callback;
 
   // Used internally to encapsulate different members on different platforms.
   class PlatformDelegate : public base::RefCountedThreadSafe<PlatformDelegate> {
    public:
@@ skipping 31 matching lines @@
     bool is_cancelled() const {
       return cancelled_;
     }
 
    private:
     scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
     bool cancelled_;
   };
 
   FilePathWatcher();
-  virtual ~FilePathWatcher();
+  ~FilePathWatcher();
 
   // A callback that always cleans up the PlatformDelegate, either when executed
   // or when deleted without having been executed at all, as can happen during
   // 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.
   //
   // 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);
 
  private:
   scoped_refptr<PlatformDelegate> impl_;
 
+  SequenceChecker sequence_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_PATH_WATCHER_H_