sync_unit_tests: add test for unknown field retention.

chrome/browser/sync/util/protobuf_unittest.cc

+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <string>
+#include <vector>
+
+#include "chrome/browser/sync/protocol/test.pb.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+TEST(SyncProtobufTest, TestUnknownFields) {
+  // This tests ensures that we retain unknown fields in protocol buffers by
+  // serialising UnknownFieldsTestB, which is a superset of UnknownFieldsTestA,
+  // and checking we get back to the same message after parsing/serialising via
+  // UnknownFieldsTestA.
+  sync_pb::UnknownFieldsTestA a;
+  sync_pb::UnknownFieldsTestB b;
+  sync_pb::UnknownFieldsTestB b2;
+
+  b.set_foo(true);
+  b.set_bar(true);
+  std::string serialized;
+  ASSERT_TRUE(b.SerializeToString(&serialized));
+  ASSERT_TRUE(a.ParseFromString(serialized));
+  ASSERT_TRUE(a.foo());
+  std::string serialized2;
+  ASSERT_TRUE(a.SerializeToString(&serialized2));
+  ASSERT_TRUE(b2.ParseFromString(serialized2));
+  ASSERT_TRUE(b2.foo());
+  ASSERT_TRUE(b2.bar());
+}
+
+}  // namespace