Remove BackForwardClient, cleanup starting a history navigation

Source/core/loader/EmptyClients.h

Index: Source/core/loader/EmptyClients.h
diff --git a/Source/core/loader/EmptyClients.h b/Source/core/loader/EmptyClients.h
index 7a6a3550afb198f570030f955cfd72ffa751e35f..00dd95897ae5f00ccc729ed786541687b99766fe 100644
--- a/Source/core/loader/EmptyClients.h
+++ b/Source/core/loader/EmptyClients.h
@@ -32,7 +32,6 @@
 #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"
@@ -325,13 +324,6 @@ public:
     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;