sync: Improve handling of bad UniquePos (retry)

sync/engine/syncer_util.h

Index: sync/engine/syncer_util.h
diff --git a/sync/engine/syncer_util.h b/sync/engine/syncer_util.h
index 575ab11d37e279de8cd08e2ed79a87513664460f..f39ad4b195ee75fd8dbf798cc7de49d85b960692 100644
--- a/sync/engine/syncer_util.h
+++ b/sync/engine/syncer_util.h
@@ -12,6 +12,7 @@
 #include <string>
 #include <vector>
 
+#include "sync/base/sync_export.h"
 #include "sync/engine/syncer.h"
 #include "sync/engine/syncer_types.h"
 #include "sync/syncable/entry_kernel.h"
@@ -58,12 +59,14 @@ UpdateAttemptResponse AttemptToUpdateEntry(
 //
 // Will return an invalid position if no valid position can be constructed, or
 // if this type does not support positioning.
-UniquePosition GetUpdatePosition(const sync_pb::SyncEntity& update,
-                                 const std::string& suffix);
+SYNC_EXPORT_PRIVATE UniquePosition GetUpdatePosition(
+    const sync_pb::SyncEntity& update,
+    const std::string& suffix);
 
 // Fetch the cache_guid and item_id-based unique bookmark tag from an update.
 // Will return an empty string if someting unexpected happens.
-std::string GetUniqueBookmarkTagFromUpdate(const sync_pb::SyncEntity& update);
+SYNC_EXPORT_PRIVATE std::string GetUniqueBookmarkTagFromUpdate(
+    const sync_pb::SyncEntity& update);
 
 // Pass in name to avoid redundant UTF8 conversion.
 void UpdateServerFieldsFromUpdate(