Fix -Wnon-virtual-dtor compiler warnings.

fpdfsdk/include/pdfwindow/PWL_IconList.h

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
  
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef _PWL_IconList_H_
 #define _PWL_IconList_H_
 
 class IPWL_IconList_Notify;
 class CPWL_IconList_Item;
 class CPWL_IconList_Content;
 class CPWL_IconList;
 class CPWL_Label;
 
 class IPWL_IconList_Notify
 {
 public:
+        virtual ~IPWL_IconList_Notify() { }
         virtual void                                            OnNoteListSelChanged(FX_INT32 nItemIndex) = 0;
 };
 
 class CPWL_IconList_Item : public CPWL_Wnd
 {
 public:
         CPWL_IconList_Item();
         virtual ~CPWL_IconList_Item();
 
         virtual CFX_ByteString                          GetClassName() const;
@@ skipping 87 matching lines @@
         virtual void                                            OnNotify(CPWL_Wnd* pWnd, FX_DWORD msg, FX_INTPTR wParam = 0, FX_INTPTR lParam = 0);
 
 private:
         CPWL_IconList_Content*                          m_pListContent;
         FX_INT32                                                        m_nListCount;
 };
  
 #endif //_PWL_IconList_H_