[SyncFS] Add MetadataDatabase::UpdateTracker

chrome/browser/sync_file_system/drive_backend/tracker_set.h

 // Copyright 2013 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_SYNC_FILE_SYSTEM_DRIVE_BACKEND_TRACKER_SET_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_TRACKER_SET_H_
 
 #include <set>
 
 namespace sync_file_system {
@@ skipping 15 matching lines @@
   TrackerSet();
   ~TrackerSet();
 
   bool has_active() const { return !!active_tracker_; }
   void Insert(FileTracker* tracker);
   void Erase(FileTracker* tracker);
   void Activate(FileTracker* tracker);
   void Inactivate(FileTracker* tracker);
 
   const FileTracker* active_tracker() const { return active_tracker_; }
+  FileTracker* active_tracker() { return active_tracker_; }
   const RawTrackerSet& tracker_set() const { return tracker_set_; }
 
   iterator begin() { return tracker_set_.begin(); }
   iterator end() { return tracker_set_.end(); }
   const_iterator begin() const { return tracker_set_.begin(); }
   const_iterator end() const { return tracker_set_.end(); }
   bool empty() const { return tracker_set_.empty(); }
 
  private:
   FileTracker* active_tracker_;
   RawTrackerSet tracker_set_;
 };
 
 }  // namespace drive_backend
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_TRACKER_SET_H_