fix build issue on Linux with GCC 4.1.2...

webkit/port/history/BackForwardList.h

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  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
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 39 matching lines @@
 
 // NOTE: We don't have all the methods in the trunk version of BackForwardList.
 // It seems some are not used except in Mac-specific code, so we can get away
 // without them.  They've been completely removed from our version so that we
 // can immediately tell from compile failures if WebCore starts using them.
 
 // A delegate class that's responsible for doing most of the work of the
 // back-forward list.
 class BackForwardListClient {
 public:
+    virtual ~BackForwardListClient() {}
     virtual void didAddHistoryItem(HistoryItem* item) = 0;
     virtual void willGoToHistoryItem(HistoryItem* item) = 0;
     virtual HistoryItem* itemAtIndex(int index) = 0;
     virtual void goToItemAtIndexAsync(int index) = 0;
     virtual int backListCount() = 0;
     virtual int forwardListCount() = 0;
 };
 
 class BackForwardList : public RefCounted<BackForwardList> {
 public: 
@@ skipping 69 matching lines @@
 
     // Settings.cpp requires an entries() method that returns a
     // HistoryItemVector reference, but we don't actually use it.
     HistoryItemVector m_entries_not_used;
 
 }; //class BackForwardList
     
 }; //namespace WebCore
 
 #endif //BACKFORWARDLIST_H