Sync: Change Local IDs to GUID based to avoid ID collision

sync/syncable/parent_child_index.cc

Index: sync/syncable/parent_child_index.cc
diff --git a/sync/syncable/parent_child_index.cc b/sync/syncable/parent_child_index.cc
index a144e6c65503f80ab6e45f7d8a5373f305a55533..d9c0052cdf5e131c105fec813ab7c6a264ef7ec9 100644
--- a/sync/syncable/parent_child_index.cc
+++ b/sync/syncable/parent_child_index.cc
@@ -34,7 +34,8 @@ bool ChildComparator::operator()(const EntryKernel* a,
     // Position doesn't matter.
     DCHECK(!a->ref(UNIQUE_POSITION).IsValid());
     DCHECK(!b->ref(UNIQUE_POSITION).IsValid());
-    return a->ref(ID) < b->ref(ID);
+    // Sort by META_HANDLE to ensure consistent order for testing.
+    return a->ref(META_HANDLE) < b->ref(META_HANDLE);
   }
 }