Add timestamp to infobar for stale Previews

components/previews/core/previews_features.cc

 // Copyright 2017 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/previews/core/previews_features.h"
 
 namespace previews {
 namespace features {
 
 // Enables the Offline previews on Android.
 const base::Feature kOfflinePreviews{"OfflinePreviews",
                                      base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables the Client Lo-Fi previews on Android.
 const base::Feature kClientLoFi{"ClientLoFi",
                                 base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables the Stale Previews timestamp on Previews infobars.
+const base::Feature kStalePreviewsTimestamp{"StalePreviewsTimestamp",
+                                            base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features
 }  // namespace previews