[SyncFS] Add RemoteToLocalSyncer skeleton

chrome/browser/sync_file_system/drive_backend/metadata_database.h

Index: chrome/browser/sync_file_system/drive_backend/metadata_database.h
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database.h b/chrome/browser/sync_file_system/drive_backend/metadata_database.h
index dced9760c5afcab2562ce6bf4b3ed19bfdb433fa..7fcc941e6aa59a053d0150a4320ba9a5e6508c1f 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database.h
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database.h
@@ -224,6 +224,14 @@ class MetadataDatabase {
                      const FileDetails& updated_details,
                      const SyncStatusCallback& callback);
 
+  // Returns true if there is a normal priority dirty tracker.
+  // Assigns the dirty tracker if exists and |tracker| is non-NULL.
+  bool GetNormalPriorityDirtyTracker(FileTracker* tracker);
+
+  // Returns true if there is a low priority dirty tracker.
+  // Assigns the dirty tracker if exists and |tracker| is non-NULL.
+  bool GetLowPriorityDirtyTracker(FileTracker* tracker);
+
  private:
   friend class ListChangesTaskTest;
   friend class MetadataDatabaseTest;