Make largest_changestamp setter/getter asynchronous.

chrome/browser/chromeos/drive/drive_feed_loader.h

Index: chrome/browser/chromeos/drive/drive_feed_loader.h
===================================================================
--- chrome/browser/chromeos/drive/drive_feed_loader.h	(revision 177026)
+++ chrome/browser/chromeos/drive/drive_feed_loader.h	(working copy)
@@ -119,6 +119,14 @@
       google_apis::GDataErrorCode status,
       scoped_ptr<google_apis::AccountMetadataFeed> account_metadata);
 
+  // Callback for DriveResourceMetadata::GetLargestChangestamp.
+  // Compares |remote_changestamp| and |local_changestamp| and triggers
+  // LoadFromServer if necessary.
+  void CompareChangestampsAndLoadIfNeeded(
+      const FileOperationCallback& callback,
+      int64 remote_changestamp,
+      int64 local_changestamp);
+
   // Callback for handling response from |DriveAPIService::GetApplicationInfo|.
   // If the application list is successfully parsed, passes the list to
   // Drive webapps registry.