[Sync] Nest UserEvent message classes within UserEventSpecifics.

components/translate/core/common/translation_logging_helper_unittest.cc

 // Copyright 2017 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 "components/translate/core/common/translation_logging_helper.h"
 
 #include <string>
 
 #include "base/logging.h"
 #include "components/metrics/proto/translate_event.pb.h"
 #include "components/sync/protocol/user_event_specifics.pb.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using metrics::TranslateEventProto;
-using sync_pb::Translation;
+using Translation = sync_pb::UserEventSpecifics::Translation;
 
 void EqualTranslationProto(const Translation& first,
                            const Translation& second) {
   EXPECT_EQ(first.from_language_code(), second.from_language_code());
   EXPECT_EQ(first.to_language_code(), second.to_language_code());
   EXPECT_EQ(first.interaction(), second.interaction());
 }
 
 namespace translate {
 
@@ skipping 54 matching lines @@
   translation_event.set_event_type(TranslateEventProto::DISABLED_BY_RANKER);
   // The user event.
   sync_pb::UserEventSpecifics user_specifics;
   const bool needs_logging =
       ConstructTranslateEvent(100, translation_event, &user_specifics);
   // We don't expect the event to be logged.
   EXPECT_FALSE(needs_logging);
 }
 
 }  // namespace translate