drive: Pass through AboutResouce from server among callbacks in ChangeListLoader.

chrome/browser/chromeos/drive/change_list_loader.h

Index: chrome/browser/chromeos/drive/change_list_loader.h
diff --git a/chrome/browser/chromeos/drive/change_list_loader.h b/chrome/browser/chromeos/drive/change_list_loader.h
index 856d79bc7bfd08c43ae00b9fccdcf8c61412437b..51bdcca70622f87e7bf41d7ba7e2d9ee650b6928 100644
--- a/chrome/browser/chromeos/drive/change_list_loader.h
+++ b/chrome/browser/chromeos/drive/change_list_loader.h
@@ -237,6 +237,10 @@ class ChangeListLoader {
   // Indicates whether there is a feed refreshing server request is in flight.
   bool refreshing_;
 
+  // Resource ID for the user's "My Drive" root. This must be retrieved from
+  // the server.
+  std::string drive_root_resource_id_;
+
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<ChangeListLoader> weak_ptr_factory_;