Use bookmark creation date fallback for 6 weeks after installing M54

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 {
 
@@ skipping 14 matching lines @@
 // The pref name for today's count of interactive requests for article
 // thumbnails, so far.
 extern const char kSnippetThumbnailsInteractiveRequestCount[];
 // The pref name for the current day for the counter of requests for article
 // thumbnails.
 extern const char kSnippetThumbnailsRequestsDay[];
 
 extern const char kDismissedRecentOfflineTabSuggestions[];
 extern const char kDismissedDownloadSuggestions[];
 
+// The pref name for the time when M54 was first started on the device.
+extern const char kBookmarksFirstM54Start[];
+
 }  // namespace prefs
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_PREF_NAMES_H_