drive: Update directory changestamp after "fast fetch" for the content.

chrome/browser/chromeos/drive/change_list_loader.cc

Index: chrome/browser/chromeos/drive/change_list_loader.cc
diff --git a/chrome/browser/chromeos/drive/change_list_loader.cc b/chrome/browser/chromeos/drive/change_list_loader.cc
index d028c72c8323b85fdffb3e028064c643da9dcadf..d9ce6d8f221ca6bfb60f7901c2f4d70eaf5023d6 100644
--- a/chrome/browser/chromeos/drive/change_list_loader.cc
+++ b/chrome/browser/chromeos/drive/change_list_loader.cc
@@ -751,8 +751,12 @@ void ChangeListLoader::ScheduleRun(
   // can check that the directory is being fetched.
   pending_load_callback_[resource_id].push_back(
       base::Bind(&util::EmptyFileOperationCallback));
+
+  DirectoryFetchInfo new_directory_fetch_info(
+      directory_fetch_info.resource_id(),
+      last_known_remote_changestamp_);

[satorux1, 2013/04/03 07:14:07]

not sure using last_known_remote_changestamp_ is correct.
last_known_remote_changestamp_ could be 0?

Maybe we should call LoadDirectoryFromServer()? Then, the latest remote
changestamp will be retrieved from the server.

[kinaba, 2013/04/03 07:58:25]

If it is 0 we are exiting the function in the if-statement above
(it could be argued that the if-statement is wrong, though...)
Ideally we want the latest value, but I think it is still ok using
|last_known_remote_changestamp_| here.

- Getting changestamp takes hundreds of milliseconds that we want to avoid if
possible.

- This call is reached only when a normal feed fetching operation, which should
update |last_known_remote_changestamp_|, is already in-flight.

- There is a chance that it is reached in the dangerous time window before "the
normal operation" updates changestamp, but
-- it does not happen during initial feed loading (users cannot initiate another
fast-fetch until the update by root directory fetching is finished.)
-- if it is being racy with delta feed fetching, observing an old value has the
same effect as just the directory listing has started slightly earlier than the
delta fetching; so it shouldn't be a big deal.

What do you think?

[satorux1, 2013/04/04 08:30:47]

See above.
Sounds reasonable. Could you add some comment why we are using
last_known_remote_changestamp_ here?

   DoLoadDirectoryFromServer(
-      directory_fetch_info,
+      new_directory_fetch_info,
       base::Bind(&ChangeListLoader::OnDirectoryLoadComplete,
                  weak_ptr_factory_.GetWeakPtr(),
                  directory_fetch_info,