[Retry][SyncFS] Implement LargestKnownChangeID handling

chrome/browser/sync_file_system/drive_backend/metadata_database.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_METADATA_DATABASE_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_METADATA_DATABASE_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 317 matching lines @@
   bool ShouldKeepDirty(const FileTracker& tracker) const;
 
   bool HasDisabledAppRoot(const FileTracker& tracker) const;
   bool HasActiveTrackerForFileID(const std::string& file_id) const;
   bool HasActiveTrackerForPath(int64 parent_tracker,
                                const std::string& title) const;
 
   void WriteToDatabase(scoped_ptr<leveldb::WriteBatch> batch,
                        const SyncStatusCallback& callback);
 
+  bool HasNewerFileMetadata(const std::string& file_id, int64 change_id);
+
   scoped_refptr<base::SequencedTaskRunner> task_runner_;
   scoped_ptr<leveldb::DB> db_;
 
   scoped_ptr<ServiceMetadata> service_metadata_;
+  int64 largest_known_change_id_;
 
   FileByID file_by_id_;  // Owned.
   TrackerByID tracker_by_id_;  // Owned.
 
   // Maps FileID to trackers.  The active tracker must be unique per FileID.
   // This must be updated when updating |active| field of a tracker.
   TrackersByFileID trackers_by_file_id_;  // Not owned.
 
   // Maps AppID to the app-root tracker.
   // This must be updated when a tracker is registered/unregistered as an
@@ skipping 15 matching lines @@
 
   base::WeakPtrFactory<MetadataDatabase> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MetadataDatabase);
 };
 
 }  // namespace drive_backend
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_METADATA_DATABASE_H_