[SyncFS] Implement methods to handle TrackerIDSet by FileID

chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h

Index: chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
index 12f8763b9718f655f714b474923b1add6be34ca5..ff0ee9bbe8a8ed4587e5e3b84b2c42158666efac 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
@@ -78,6 +78,15 @@ class MetadataDatabaseIndexOnDisk : public MetadataDatabaseIndexInterface {
   void RemoveFromAppIDIndex(const FileTracker& tracker,
                             leveldb::WriteBatch* batch);
 
+  // Maintain indexes from remote file IDs to tracker IDs
+  void AddToFileIDIndexes(const FileTracker& new_tracker,
+                          leveldb::WriteBatch* batch);
+  void UpdateInFileIDIndexes(const FileTracker& old_tracker,
+                             const FileTracker& new_tracker,
+                             leveldb::WriteBatch* batch);
+  void RemoveFromFileIDIndexes(const FileTracker& tracker,
+                               leveldb::WriteBatch* batch);
+
   // Maintain dirty tracker IDs.
   void AddToDirtyTrackerIndexes(const FileTracker& new_tracker,
                                 leveldb::WriteBatch* batch);
@@ -87,6 +96,11 @@ class MetadataDatabaseIndexOnDisk : public MetadataDatabaseIndexInterface {
   void RemoveFromDirtyTrackerIndexes(const FileTracker& tracker,
                                      leveldb::WriteBatch* batch);
 
+  // Returns a TrackerIDSet built from IDs which are found with given key
+  // and key prefix.
+  TrackerIDSet GetTrackerIDSetByPrefix(
+      const std::string& active_key, const std::string& key_prefix) const;
+
   // Checks if |db_| has an entry whose key is |key|.
   bool DBHasKey(const std::string& key);