Media Galleries: Refactor media scan worker function into a worker class.

chrome/browser/media_galleries/media_folder_finder.h

 // 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.
 
 #ifndef CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FOLDER_FINDER_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FOLDER_FINDER_H_
 
 #include <map>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/files/file_path.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/sequenced_worker_pool.h"
+#include "base/sequenced_task_runner.h"
 #include "chrome/browser/media_galleries/media_scan_types.h"
 
 // MediaFolderFinder scans local hard drives and look for folders that contain
 // media files.
 class MediaFolderFinder {
  public:
   typedef std::map<base::FilePath, MediaGalleryScanResult>
       MediaFolderFinderResults;
   typedef base::Callback<void(bool /*success*/,
                               const MediaFolderFinderResults& /*results*/)>
       MediaFolderFinderResultsCallback;
-  typedef base::Callback<MediaGalleryScanFileType(const base::FilePath&)>
-      FilterCallback;
 
   // |callback| will get called when the scan finishes. If the object is deleted
   // before it finishes, the scan will stop and |callback| will get called with
   // success = false.
   // MediaFolderFinder has a default set of per-platform paths to scan.
   // Override in tests with SetRootsForTesting().
   explicit MediaFolderFinder(const MediaFolderFinderResultsCallback& callback);
   virtual ~MediaFolderFinder();
 
   // Start the scan.
   virtual void StartScan();
 
  private:
   friend class MediaFolderFinderTest;
 
+  class Worker;
+  struct WorkerReply {
+    WorkerReply();
+    ~WorkerReply();
+
+    MediaGalleryScanResult scan_result;
+    std::vector<base::FilePath> new_folders;
+  };
+
   enum ScanState {
     SCAN_STATE_NOT_STARTED,
     SCAN_STATE_STARTED,
     SCAN_STATE_FINISHED,
   };
 
   void SetRootsForTesting(const std::vector<base::FilePath>& roots);
 
   void OnInitialized(const std::vector<base::FilePath>& roots);
 
   // Scan a folder from |folders_to_scan_|.
   void ScanFolder();
 
-  // Callback that returns the |scan_result| for |path| and the |new_folders|
-  // to scan in future calls to ScanFolder().
-  void GotScanResults(const base::FilePath& path,
-                      const MediaGalleryScanResult* scan_result,
-                      const std::vector<base::FilePath>* new_folders);
+  // Callback that handles the |reply| from |worker_| for a scanned |path|.
+  void GotScanResults(const base::FilePath& path, const WorkerReply& reply);
 
   const MediaFolderFinderResultsCallback results_callback_;
   MediaFolderFinderResults results_;
 
   std::vector<base::FilePath> folders_to_scan_;
   ScanState scan_state_;
 
-  // Token to make sure all calls with |filter_callback_| are on the same
-  // sequence.
-  base::SequencedWorkerPool::SequenceToken token_;
+  scoped_refptr<base::SequencedTaskRunner> worker_task_runner_;
 
-  // Callback used to filter through files and make sure they are media files.
-  FilterCallback filter_callback_;
+  // Owned by MediaFolderFinder, but lives on |worker_task_runner_|.
+  Worker* worker_;
 
   // Set of roots to scan for testing.
   bool has_roots_for_testing_;
   std::vector<base::FilePath> roots_for_testing_;
 
   base::WeakPtrFactory<MediaFolderFinder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaFolderFinder);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FOLDER_FINDER_H_