1 files changed, 14 insertions, 0 deletions
diff --git a/net/tools/testserver/chromiumsync.py b/net/tools/testserver/chromiumsync.py
index 62d1bf7..b678238 100755
--- a/net/tools/testserver/chromiumsync.py
+++ b/net/tools/testserver/chromiumsync.py
@@ -487,6 +487,18 @@ class SyncDataModel(object):
     # batch, even if that item was filtered out.
     return (batch[-1].version, filtered, len(new_changes) - len(batch))
 
+  def _CopyOverImmutableFields(self, entry):
+    """Preserve immutable fields by copying pre-commit state.
+    
+    Args:
+      entry: A sync entity from the client.
+    """
+    if entry.id_string in self._entries:
+      if self._entries[entry.id_string].HasField(
+          'server_defined_unique_tag'):
+        entry.server_defined_unique_tag = (
+            self._entries[entry.id_string].server_defined_unique_tag)
+
   def _CheckVersionForCommit(self, entry):
     """Perform an optimistic concurrency check on the version number.
 
@@ -599,6 +611,8 @@ class SyncDataModel(object):
     if not self._CheckParentIdForCommit(entry):
       return None
 
+    self._CopyOverImmutableFields(entry);  
+
     # At this point, the commit is definitely going to happen.
 
     # Deletion works by storing a limited record for an entry, called a