drive: Also lock SearchOperation when locking ChangeListLoader

chrome/browser/chromeos/drive/file_system.h

Index: chrome/browser/chromeos/drive/file_system.h
diff --git a/chrome/browser/chromeos/drive/file_system.h b/chrome/browser/chromeos/drive/file_system.h
index 9d137302e80150b7b996a1c31bd9e6e33dfcfe86..da003fe1c38c33a9b6011ea7dcf28610d5930750 100644
--- a/chrome/browser/chromeos/drive/file_system.h
+++ b/chrome/browser/chromeos/drive/file_system.h
@@ -37,6 +37,7 @@ class JobScheduler;
 namespace internal {
 class ChangeListLoader;
 class FileCache;
+class LoaderController;
 class ResourceMetadata;
 class SyncClient;
 }  // namespace internal
@@ -255,6 +256,9 @@ class FileSystem : public FileSystemInterface,
   // Error of the last update check.
   FileError last_update_check_error_;
 
+  // Used to control ChangeListLoader.
+  scoped_ptr<internal::LoaderController> loader_controller_;
+
   // The loader is used to load the change lists.
   scoped_ptr<internal::ChangeListLoader> change_list_loader_;