[Sync] Add a sanity integration test for USS.

components/sync/test/fake_server/unique_client_entity.h

Index: components/sync/test/fake_server/unique_client_entity.h
diff --git a/components/sync/test/fake_server/unique_client_entity.h b/components/sync/test/fake_server/unique_client_entity.h
index acb3cec53a2101cad035a4d101589d039f3f1880..5fe819dcd48ebf7c5cde6d88b33b31ce22ec83d5 100644
--- a/components/sync/test/fake_server/unique_client_entity.h
+++ b/components/sync/test/fake_server/unique_client_entity.h
@@ -28,10 +28,10 @@ namespace fake_server {
 class UniqueClientEntity : public FakeServerEntity {
  public:
   UniqueClientEntity(const std::string& id,
+                     const std::string& client_defined_unique_tag,
                      syncer::ModelType model_type,
                      int64_t version,
                      const std::string& name,
-                     const std::string& client_defined_unique_tag,
                      const sync_pb::EntitySpecifics& specifics,
                      int64_t creation_time,
                      int64_t last_modified_time);
@@ -59,7 +59,6 @@ class UniqueClientEntity : public FakeServerEntity {
 
  private:
   // These member values have equivalent fields in SyncEntity.
-  std::string client_defined_unique_tag_;
   int64_t creation_time_;
   int64_t last_modified_time_;
 };