Keep WKWebView control group users in the control group

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 52 matching lines @@
 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";
 
+// True if the previous session was selected into the WKWebView control group.
+const char kLastSessionUsedWKWebViewControlGroup[] =
+    "ios.wkwebview_trial.was_control";
+
 // 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";
 
 // A boolean pref set to true if prediction of network actions is allowed.
 // Actions include prerendering of web pages.
 // NOTE: The "dns_prefetching.enabled" value is used so that historical user
 // preferences are not lost.
 const char kNetworkPredictionEnabled[] = "dns_prefetching.enabled";
@@ skipping 41 matching lines @@
 // authorization alert.
 const char kOmniboxGeolocationLastAuthorizationAlertVersion[] =
     "ios.omnibox.geolocation_last_authorization_alert_version";
 
 // Integer which contains the timestamp at which the "Rate This App" dialog was
 // last shown.
 const char kRateThisAppDialogLastShownTime[] =
     "ios.ratethisapp.dialog_last_shown_time";
 
 }  // namespace prefs