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

components/ntp_snippets/pref_names.h

 // 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.
 
 #ifndef COMPONENTS_NTP_SNIPPETS_PREF_NAMES_H_
 #define COMPONENTS_NTP_SNIPPETS_PREF_NAMES_H_
 
 namespace ntp_snippets {
 namespace prefs {
 
 // If set to false, remote suggestions are completely disabled. This is set by
 // an enterprise policy.
 extern const char kEnableSnippets[];
 
 // The pref name under which remote suggestion categories (including their ID
 // and title) are stored.
 extern const char kRemoteSuggestionCategories[];
 
 // The pref name for the last time when a background fetch was attempted.
 extern const char kSnippetLastFetchAttempt[];
 // The pref name for the currently applied minimal interval between two
 // successive soft background fetches that react to user activity (such as
-// opening an NTP).
+// opening Chrome).
 extern const char kSnippetSoftFetchingIntervalOnUsageEvent[];
+// The pref name for the currently applied minimal interval between two
+// successive soft brackground fetches when the New Tab Page is opened.
+extern const char kSnippetSoftFetchingIntervalOnNtpOpened[];
 
 // The pref name for the currently-scheduled background fetching interval when
 // there is WiFi connectivity.
 extern const char kSnippetPersistentFetchingIntervalWifi[];
 // The pref name for the currently-scheduled background fetching interval when
 // there is no WiFi connectivity.
 extern const char kSnippetPersistentFetchingIntervalFallback[];
 
 // The pref name for today's count of RemoteSuggestionsFetcher requests, so far.
 extern const char kSnippetFetcherRequestCount[];
@@ skipping 44 matching lines @@
 
 // The pref name for the current order of categories and their clicks.
 extern const char kClickBasedCategoryRankerOrderWithClicks[];
 // The pref name for the time when last click decay has happened.
 extern const char kClickBasedCategoryRankerLastDecayTime[];
 
 }  // namespace prefs
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_PREF_NAMES_H_