Add request throttler to thumbnail fetching for articles on mobile NTP

components/ntp_snippets/request_throttler_unittest.cc

 // Copyright 2016 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/request_throttler.h"
 
 #include <memory>
 
 #include "base/strings/stringprintf.h"
 #include "components/ntp_snippets/pref_names.h"
@@ skipping 44 matching lines @@
   EXPECT_TRUE(throttler_->DemandQuotaForRequest(true));
 }
 
 TEST_F(RequestThrottlerTest, QuotaIsPerDay) {
   EXPECT_TRUE(throttler_->DemandQuotaForRequest(false));
   EXPECT_TRUE(throttler_->DemandQuotaForRequest(false));
 
   // Now fake the day pref so that the counter believes the count comes from
   // yesterday.
   int now_day = (base::Time::Now() - base::Time::UnixEpoch()).InDays();
-  test_prefs_.SetInteger(ntp_snippets::prefs::kSnippetFetcherQuotaDay,
+  test_prefs_.SetInteger(ntp_snippets::prefs::kSnippetFetcherRequestsDay,
                          now_day - 1);
 
   // The quota should get reset as the day has changed.
   EXPECT_TRUE(throttler_->DemandQuotaForRequest(false));
 }
 
 }  // namespace ntp_snippets