[Sync] Replace AttachmentIdSet with AttachmentIdList in interfaces.

sync/syncable/directory.h

Index: sync/syncable/directory.h
diff --git a/sync/syncable/directory.h b/sync/syncable/directory.h
index 98706b61cece207234d38f593d30ca6921a01394..b98328f1125d87754fd295d2fd022bb1938603c2 100644
--- a/sync/syncable/directory.h
+++ b/sync/syncable/directory.h
@@ -417,11 +417,11 @@ class SYNC_EXPORT Directory {
   // preserve sync preferences in DB on disk.
   void UnmarkDirtyEntry(WriteTransaction* trans, Entry* entry);
 
-  // Clears |id_set| and fills it with the ids of attachments that need to be
+  // Clears |ids| and fills it with the ids of attachments that need to be
   // uploaded to the sync server.
   void GetAttachmentIdsToUpload(BaseTransaction* trans,
                                 ModelType type,
-                                AttachmentIdSet* id_set);
+                                AttachmentIdList* ids);
 
  private:
   struct Kernel {