Fix -Wnon-virtual-dtor compiler warnings.

core/include/fxge/fx_font.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 _FX_FONT_H_
 #define _FX_FONT_H_
 #ifndef _FXCRT_EXTENSION_
 #include "../../include/fxcrt/fx_ext.h"
@@ skipping 225 matching lines @@
     virtual ~IFX_FontMapper() {}
 
     virtual FXFT_Face   FindSubstFont(const CFX_ByteString& face_name, FX_BOOL bTrueType, FX_DWORD flags,
                                       int weight, int italic_angle, int CharsetCP, CFX_SubstFont* pSubstFont) = 0;
 
     CFX_FontMgr*                m_pFontMgr;
 };
 class IFX_FontEnumerator
 {
 public:
+    virtual ~IFX_FontEnumerator() { }
 
     virtual void                HitFont() = 0;
 
     virtual void                Finish() = 0;
 };
 class IFX_AdditionalFontEnum
 {
 public:
+    virtual ~IFX_AdditionalFontEnum() { }
     virtual int  CountFiles() = 0;
     virtual IFX_FileStream* GetFontFile(int index) = 0;
 };
 class CFX_FontMapper : public IFX_FontMapper
 {
 public:
     CFX_FontMapper();
     virtual ~CFX_FontMapper();
     void                                SetSystemFontInfo(IFX_SystemFontInfo* pFontInfo);
     IFX_SystemFontInfo* GetSystemFontInfo()
@@ skipping 25 matching lines @@
     CFX_ByteStringArray m_FaceArray;
     IFX_SystemFontInfo* m_pFontInfo;
     FXFT_Face                   m_FoxitFaces[14];
     IFX_FontEnumerator*         m_pFontEnumerator;
 };
 class IFX_SystemFontInfo : public CFX_Object
 {
 public:
     static IFX_SystemFontInfo*  CreateDefault();
     virtual void                Release() = 0;
+
     virtual     FX_BOOL         EnumFontList(CFX_FontMapper* pMapper) = 0;
     virtual void*               MapFont(int weight, FX_BOOL bItalic, int charset, int pitch_family, FX_LPCSTR face, FX_BOOL& bExact) = 0;
     virtual void*               GetFont(FX_LPCSTR face) = 0;
     virtual FX_DWORD    GetFontData(void* hFont, FX_DWORD table, FX_LPBYTE buffer, FX_DWORD size) = 0;
     virtual FX_BOOL             GetFaceName(void* hFont, CFX_ByteString& name) = 0;
     virtual FX_BOOL             GetFontCharset(void* hFont, int& charset) = 0;
     virtual int                 GetFaceIndex(void* hFont)
     {
         return 0;
     }
     virtual void                DeleteFont(void* hFont) = 0;
     virtual void*       RetainFont(void* hFont)
     {
         return NULL;
     }
+protected:
+    ~IFX_SystemFontInfo() { }
 };
 class CFX_FolderFontInfo : public IFX_SystemFontInfo
 {
 public:
     CFX_FolderFontInfo();
     virtual ~CFX_FolderFontInfo();
     void                                AddPath(FX_BSTR path);
     virtual void                Release();
     virtual     FX_BOOL         EnumFontList(CFX_FontMapper* pMapper);
     virtual void*               MapFont(int weight, FX_BOOL bItalic, int charset, int pitch_family, FX_LPCSTR face, FX_BOOL& bExact);
@@ skipping 92 matching lines @@
 FX_RECT FXGE_GetGlyphsBBox(FXTEXT_GLYPHPOS* pGlyphAndPos, int nChars, int anti_alias, FX_FLOAT retinaScaleX = 1.0f, FX_FLOAT retinaScaleY = 1.0f);
 FX_BOOL OutputGlyph(void* dib, int x, int y, CFX_Font* pFont, double font_size,
                     CFX_AffineMatrix* pMatrix, unsigned long glyph_index, unsigned long argb);
 FX_BOOL OutputText(void* dib, int x, int y, CFX_Font* pFont, double font_size,
                    CFX_AffineMatrix* pText_matrix, unsigned short const* text, unsigned long argb);
 class IFX_GSUBTable
 {
 public:
     virtual void        Release() = 0;
     virtual FX_BOOL GetVerticalGlyph(FX_DWORD glyphnum, FX_DWORD* vglyphnum) = 0;
+
+protected:
+     ~IFX_GSUBTable() { }
 };
 IFX_GSUBTable* FXGE_CreateGSUBTable(CFX_Font* pFont);
 #endif