Allow FilePathWatcher to be used from sequenced tasks.

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"
+#include "base/sequenced_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
@@ skipping 13 matching lines @@
    public:
     PlatformDelegate();
 
     // Start watching for the given |path| and notify |delegate| about changes.
     virtual bool Watch(const FilePath& path,
                        bool recursive,
                        const Callback& callback) WARN_UNUSED_RESULT = 0;
 
     // Stop watching. This is called from FilePathWatcher's dtor in order to
     // 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();
 
-    scoped_refptr<base::SingleThreadTaskRunner> task_runner() const {
+    scoped_refptr<SequencedTaskRunner> task_runner() const {
       return task_runner_;
     }
 
-    void set_task_runner(scoped_refptr<base::SingleThreadTaskRunner> runner) {
+    void set_task_runner(scoped_refptr<SequencedTaskRunner> runner) {
       task_runner_ = std::move(runner);
     }
 
     // Must be called before the PlatformDelegate is deleted.
     void set_cancelled() {
       cancelled_ = true;
     }
 
     bool is_cancelled() const {
       return cancelled_;
     }
 
    private:
-    scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+    scoped_refptr<SequencedTaskRunner> task_runner_;
     bool cancelled_;
   };
 
   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. Set |recursive| to true, to watch |path| and its
-  // children. The callback will be invoked on the same thread. Returns true on
-  // success.
+  // called at most once. Set |recursive| to true to watch |path| and its
+  // children. The callback will be invoked on the same sequence. Returns true
+  // on success.
   //
   // On POSIX, this must be called from a thread that supports
   // FileDescriptorWatcher.
   //
   // 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_