drive: Rewrite UpdateOpreation to access cache/metadata on the blocking pool

chrome/browser/chromeos/drive/file_system/operations.cc

Index: chrome/browser/chromeos/drive/file_system/operations.cc
diff --git a/chrome/browser/chromeos/drive/file_system/operations.cc b/chrome/browser/chromeos/drive/file_system/operations.cc
index 7ebb8e4d6f18c899999e2b1dbc5f3ea1557f3b5c..392cb180dcc84a23dfe0b2e969305c4d42116342 100644
--- a/chrome/browser/chromeos/drive/file_system/operations.cc
+++ b/chrome/browser/chromeos/drive/file_system/operations.cc
@@ -63,8 +63,11 @@ void Operations::Init(OperationObserver* observer,
       new TouchOperation(blocking_task_runner, observer, scheduler, metadata));
   download_operation_.reset(new DownloadOperation(
       blocking_task_runner, observer, scheduler, metadata, cache));
-  update_operation_.reset(
-      new UpdateOperation(observer, scheduler, metadata, cache));
+  update_operation_.reset(new UpdateOperation(blocking_task_runner,
+                                              observer,
+                                              scheduler,
+                                              metadata,
+                                              cache));
   search_operation_.reset(
       new SearchOperation(blocking_task_runner, scheduler, metadata));
 }