Make CanOpenBeforeUnloadConfirmPanel a RuntimeEnabledFeature

Source/web/ChromeClientImpl.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 367 matching lines @@
         frame->client()->didAddMessageToConsole(
             WebConsoleMessage(static_cast<WebConsoleMessage::Level>(level), message),
             sourceID,
             lineNumber,
             stackTrace);
     }
 }
 
 bool ChromeClientImpl::canOpenBeforeUnloadConfirmPanel()
 {
-    return !!m_webView->client();
+    return RuntimeEnabledFeatures::canOpenBeforeUnloadConfirmPanelEnabled() && !!m_webView->client();
 }
 
 bool ChromeClientImpl::openBeforeUnloadConfirmPanelDelegate(LocalFrame* frame, const String& message)
 {
     notifyPopupOpeningObservers();
     WebLocalFrameImpl* webframe = WebLocalFrameImpl::fromFrame(frame);
 
     WebDataSource* ds = webframe->provisionalDataSource();
     bool isReload = ds && (ds->navigationType() == WebNavigationTypeReload);
 
@@ skipping 567 matching lines @@
     for (const auto& observer : observers)
         observer->willOpenPopup();
 }
 
 FloatSize ChromeClientImpl::elasticOverscroll() const
 {
     return m_webView->elasticOverscroll();
 }
 
 } // namespace blink