Add request throttler to thumbnail fetching for articles on mobile NTP

components/ntp_snippets/pref_names.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/pref_names.h"
 
 namespace ntp_snippets {
 namespace prefs {
 
 const char kEnableSnippets[] = "ntp_snippets.enable";
 
 const char kSnippetHosts[] = "ntp_snippets.hosts";
 
 const char kSnippetFetcherQuotaDay[] =
     "ntp.request_throttler.suggestion_fetcher.day";
 const char kSnippetFetcherQuotaCount[] =
     "ntp.request_throttler.suggestion_fetcher.count";
+const char kSnippetFetcherInteractiveQuotaCount[] =
+    "ntp.request_throttler.suggestion_fetcher.interactive_count";
+
+const char kSnippetThumbnailsQuotaDay[] =
+    "ntp.request_throttler.suggestion_thumbnails.day";
+const char kSnippetThumbnailsQuotaCount[] =
+    "ntp.request_throttler.suggestion_thumbnails.count";
+const char kSnippetThumbnailsInteractiveQuotaCount[] =
+    "ntp.request_throttler.suggestion_thumbnails.interactive_count";
 
 }  // namespace prefs
 }  // namespace ntp_snippets