[NTP Snippets] Cleanups from clang-tidy

components/ntp_snippets/ntp_snippets_service_unittest.cc

 // Copyright 2015 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/ntp_snippets/ntp_snippets_service.h"
 
 #include <memory>
 #include <utility>
 #include <vector>
 
@@ skipping 36 matching lines @@
 using image_fetcher::ImageFetcher;
 using image_fetcher::ImageFetcherDelegate;
 using testing::ElementsAre;
 using testing::Eq;
 using testing::InSequence;
 using testing::Invoke;
 using testing::IsEmpty;
 using testing::Mock;
 using testing::MockFunction;
 using testing::NiceMock;
-using testing::Return;
 using testing::SaveArg;
 using testing::SizeIs;
 using testing::StartsWith;
 using testing::WithArgs;
 using testing::_;
 
 namespace ntp_snippets {
 
 namespace {
 
@@ skipping 976 matching lines @@
              end = base::Time::FromTimeT(456);
   base::Callback<bool(const GURL& url)> filter;
   service->ClearHistory(begin, end, filter);
 
   EXPECT_THAT(service->GetSnippetsForTesting(articles_category()), IsEmpty());
   EXPECT_THAT(service->GetDismissedSnippetsForTesting(articles_category()),
               IsEmpty());
 }
 
 }  // namespace ntp_snippets