Remove the old didFirstVisuallyNonEmptyLayout hook.

Source/core/loader/EmptyClients.h

 /*
  * Copyright (C) 2006 Eric Seidel (eric@webkit.org)
  * Copyright (C) 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 184 matching lines @@
     void dispatchDidReceiveServerRedirectForProvisionalLoad() override {}
     void dispatchWillClose() override {}
     void dispatchDidStartProvisionalLoad(double triggeringEventTime) override {}
     void dispatchDidReceiveTitle(const String&) override {}
     void dispatchDidChangeIcons(IconType) override {}
     void dispatchDidCommitLoad(HistoryItem*, HistoryCommitType) override {}
     void dispatchDidFailProvisionalLoad(const ResourceError&, HistoryCommitType) override {}
     void dispatchDidFailLoad(const ResourceError&, HistoryCommitType) override {}
     void dispatchDidFinishDocumentLoad(bool) override {}
     void dispatchDidFinishLoad() override {}
-    void dispatchDidFirstVisuallyNonEmptyLayout() override {}
     void dispatchDidChangeThemeColor() override {}
 
     NavigationPolicy decidePolicyForNavigation(const ResourceRequest&, DocumentLoader*, NavigationPolicy) override;
 
     void dispatchWillSendSubmitEvent(HTMLFormElement*) override;
     void dispatchWillSubmitForm(HTMLFormElement*) override;
 
     void didStartLoading(LoadStartType) override {}
     void progressEstimateChanged(double) override {}
     void didStopLoading() override {}
@@ skipping 108 matching lines @@
     ~EmptyDragClient() override {}
     DragDestinationAction actionMaskForDrag(DragData*) override { return DragDestinationActionNone; }
     void startDrag(DragImage*, const IntPoint&, const IntPoint&, DataTransfer*, LocalFrame*, bool) override {}
 };
 
 CORE_EXPORT void fillWithEmptyClients(Page::PageClients&);
 
 } // namespace blink
 
 #endif // EmptyClients_h