[iOS] Upstream some stability code

ios/chrome/browser/pref_names.cc

 // Copyright 2014 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 "ios/chrome/browser/pref_names.h"
 
 namespace ios {
 namespace prefs {
 
 // Preferences in ios::prefs:: must have the same value as the corresponding
@@ skipping 29 matching lines @@
 // Boolean which indicates if the user has already set a "do not backup" bit to
 // the OTR Profiles's state stash path to ensure that the folder is not
 // automatically synced to iCloud/iTunes.
 const char kOTRStashStatePathSystemBackupExcluded[] =
     "ios.otr_stash_state_path_system_backup_excluded";
 
 // Whether Chrome should attempt to hand off the current URL to other Apple
 // devices that share an iCloud account.
 const char kIosHandoffToOtherDevices[] = "ios.handoff_to_other_devices";
 
+// True if the previous session exited cleanly.
+// This can be different from kStabilityExitedCleanly, because the last run of
+// the program may not have included a browsing session, and thus the last run
+// of the program may have happened after the run that included the last
+// session.
+const char kLastSessionExitedCleanly[] =
+    "ios.user_experience_metrics.last_session_exited_cleanly";
+
 // Preference that hold a boolean indicating whether metrics reporting should
 // be limited to wifi (when enabled).
 const char kMetricsReportingWifiOnly[] =
     "ios.user_experience_metrics.wifi_only";
 
 // Preference that hold a boolean indicating whether network prediction should
 // be limited to wifi (when enabled).
 const char kNetworkPredictionWifiOnly[] = "ios.dns_prefetching.wifi_only";
 
 // Which bookmarks folder should be visible on the new tab page v4.
@@ skipping 30 matching lines @@
 // authorization.
 extern const char kOmniboxGeolocationAuthorizationState[] =
     "ios.omnibox.geolocation_authorization_state";
 
 // String which contains the application version when we last showed the
 // authorization alert.
 extern const char kOmniboxGeolocationLastAuthorizationAlertVersion[] =
     "ios.omnibox.geolocation_last_authorization_alert_version";
 
 }  // namespace prefs