Remove BackForwardClient, cleanup starting a history navigation

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 14 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef EmptyClients_h
 #define EmptyClients_h
 
 #include "core/editing/UndoStep.h"
 #include "core/inspector/InspectorClient.h"
 #include "core/loader/FrameLoaderClient.h"
-#include "core/page/BackForwardClient.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/ContextMenuClient.h"
 #include "core/page/DragClient.h"
 #include "core/page/EditorClient.h"
 #include "core/page/FocusType.h"
 #include "core/page/Page.h"
 #include "core/page/SpellCheckerClient.h"
 #include "core/page/StorageClient.h"
 #include "platform/DragImage.h"
 #include "platform/geometry/FloatRect.h"
@@ skipping 272 matching lines @@
 class EmptyInspectorClient final : public InspectorClient {
     WTF_MAKE_NONCOPYABLE(EmptyInspectorClient); WTF_MAKE_FAST_ALLOCATED;
 public:
     EmptyInspectorClient() { }
     virtual ~EmptyInspectorClient() { }
 
     virtual void highlight() override { }
     virtual void hideHighlight() override { }
 };
 
-class EmptyBackForwardClient final : public BackForwardClient {
-public:
-    virtual int backListCount() override { return 0; }
-    virtual int forwardListCount() override { return 0; }
-    virtual int backForwardListCount() override { return 0; }
-};
-
 class EmptyStorageClient final : public StorageClient {
 public:
     virtual PassOwnPtr<StorageNamespace> createSessionStorageNamespace() override;
     virtual bool canAccessStorage(LocalFrame*, StorageType) const override { return false; }
 };
 
 void fillWithEmptyClients(Page::PageClients&);
 
 }
 
 #endif // EmptyClients_h