Fix -Wnon-virtual-dtor compiler warnings.

fpdfsdk/include/pdfwindow/PWL_Edit.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_EDIT_H_
 #define _PWL_EDIT_H_
 
 class IPWL_Filler_Notify;
 class CPWL_Edit;
 class IPWL_SpellCheck;
 
 class IPWL_Filler_Notify
 {
 public:
+        virtual ~IPWL_Filler_Notify() { }
         virtual void                                    QueryWherePopup(void* pPrivateData, FX_FLOAT fPopupMin,FX_FLOAT fPopupMax, 
                                                                                 FX_INT32 & nRet, FX_FLOAT & fPopupRet) = 0; //nRet: (0:bottom 1:top)
         virtual void                                    OnBeforeKeyStroke(FX_BOOL bEditOrList, void* pPrivateData, FX_INT32 nKeyCode,
                                                                                 CFX_WideString & strChange, const CFX_WideString& strChangeEx, 
                                                                                 int nSelStart, int nSelEnd,
                                                                                 FX_BOOL bKeyDown, FX_BOOL & bRC, FX_BOOL & bExit, FX_DWORD nFlag) = 0;
         virtual void                                    OnAfterKeyStroke(FX_BOOL bEditOrList, void* pPrivateData, FX_BOOL & bExit, FX_DWORD nFlag) = 0;
 };
 
 class PWL_CLASS CPWL_Edit : public CPWL_EditCtrl, public IFX_Edit_OprNotify
@@ skipping 102 matching lines @@
         FX_BOOL                                                 m_bFocus;
         CPDF_Rect                                               m_rcOldWindow;
 public:
         void                                                    AttachFFLData(void* pData) {m_pFormFiller = pData;}
 private:
         void*                                                   m_pFormFiller;
 };
 
 #endif