[remote suggestions] Add separte fetch interval for NTP open trigger

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 kRemoteSuggestionCategories[] = "ntp_snippets.remote_categories";
 
 const char kSnippetLastFetchAttempt[] =
     "ntp_snippets.last_fetch_attempt";
 
 const char kSnippetSoftFetchingIntervalOnUsageEvent[] =
     "ntp_snippets.soft_fetching_interval_on_usage_event";
 
+const char kSnippetSoftFetchingIntervalOnNtpOpened[] =
+    "ntp_snippets.soft_fetching_interval_on_ntp_opened";
+
 const char kSnippetPersistentFetchingIntervalWifi[] =
     "ntp_snippets.fetching_interval_wifi";
 
 const char kSnippetPersistentFetchingIntervalFallback[] =
     "ntp_snippets.fetching_interval_fallback";
 
 const char kSnippetFetcherRequestCount[] =
     "ntp.request_throttler.suggestion_fetcher.count";
 const char kSnippetFetcherInteractiveRequestCount[] =
     "ntp.request_throttler.suggestion_fetcher.interactive_count";
@@ skipping 37 matching lines @@
 const char kUserClassifierLastTimeToUseSuggestions[] =
     "ntp_suggestions.user_classifier.last_time_to_use_suggestions";
 
 const char kClickBasedCategoryRankerOrderWithClicks[] =
     "ntp_suggestions.click_based_category_ranker.category_order_with_clicks";
 const char kClickBasedCategoryRankerLastDecayTime[] =
     "ntp_suggestions.click_based_category_ranker.last_decay_time";
 
 }  // namespace prefs
 }  // namespace ntp_snippets