Pass blocking pool runner to CreateTemporaryFile in SyncFS v2 drive_backend

chrome/browser/sync_file_system/drive_backend/drive_backend_util.h

Index: chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
diff --git a/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h b/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
index e75481df9c949c8c1b5489d04e592e65932f80ad..0515a005a3344e17b42d0ddd890f0af2287c9309 100644
--- a/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
+++ b/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
@@ -43,8 +43,9 @@ scoped_ptr<FileMetadata> CreateDeletedFileMetadata(
     const std::string& file_id);
 
 // Creates a temporary file in |dir_path|.  This must be called on an
-// IO-allowed thread.
-webkit_blob::ScopedFile CreateTemporaryFile();
+// IO-allowed task runner, and the runner must be given as |file_task_runner|.
+webkit_blob::ScopedFile CreateTemporaryFile(
+    base::TaskRunner* file_task_runner);
 
 std::string FileKindToString(FileKind file_kind);