Fix -Wnon-virtual-dtor compiler warnings.

core/include/fpdfdoc/fpdf_ap.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 _FPDF_AP_H_
 #define _FPDF_AP_H_
 
 #include "../fxcrt/fx_basic.h"
 #include "../fpdfapi/fpdf_parser.h"
 #include "fpdf_vt.h"
 class IPVT_FontMap
 {
 public:
-
+    virtual ~IPVT_FontMap() { }
     virtual CPDF_Font*                                          GetPDFFont(FX_INT32 nFontIndex) = 0;
-
     virtual CFX_ByteString                                      GetPDFFontAlias(FX_INT32 nFontIndex) = 0;
 };
 struct CPVT_Dash {
 
     CPVT_Dash(FX_INT32 dash, FX_INT32 gap, FX_INT32 phase) : nDash(dash), nGap(gap), nPhase(phase)
     {}
 
     FX_INT32                    nDash;
 
     FX_INT32                    nGap;
@@ skipping 58 matching lines @@
             const CPDF_Point & ptOffset, FX_BOOL bContinuous, FX_WORD SubWord = 0, const CPVT_WordRange * pVisible = NULL);
 
     static CFX_ByteString                                       GenerateBorderAP(const CPDF_Rect & rect, FX_FLOAT fWidth,
             const CPVT_Color & color, const CPVT_Color & crLeftTop, const CPVT_Color & crRightBottom,
             FX_INT32 nStyle, const CPVT_Dash & dash);
 
     static CFX_ByteString                                       GenerateColorAP(const CPVT_Color & color, const FX_BOOL & bFillOrStroke);
 };
 
 #endif  // _FPDF_AP_H_