Sync FileSystem: Drop is_fetching_changes_ flag and completion_callback

chrome/browser/sync_file_system/drive_file_sync_service.h

Index: chrome/browser/sync_file_system/drive_file_sync_service.h
diff --git a/chrome/browser/sync_file_system/drive_file_sync_service.h b/chrome/browser/sync_file_system/drive_file_sync_service.h
index de30199c651d387a50fb30271f5ff24545b1e564..b3fedb03a8c61f9479780f2acb9fdda7bb0caf53 100644
--- a/chrome/browser/sync_file_system/drive_file_sync_service.h
+++ b/chrome/browser/sync_file_system/drive_file_sync_service.h
@@ -394,9 +394,7 @@ class DriveFileSyncService
   // If polling_delay_seconds_ is negative (<0) the timer won't start.
   int64 polling_delay_seconds_;
 
-  // Is set to true while the service is fetching changes for incremental
-  // sync. Polling will be disabled while this is true.
-  bool is_fetching_changes_;
+  bool has_unfetched_remote_change_;
 
   ObserverList<Observer> service_observers_;
   ObserverList<FileStatusObserver> file_status_observers_;