Fix -Wnon-virtual-dtor compiler warnings.

core/include/fxcrt/fx_stream.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_STREAM_H_
 #define _FX_STREAM_H_
 #ifndef _FX_MEMORY_H_
 #include "fx_memory.h"
@@ skipping 47 matching lines @@
 FX_BOOL         FX_File_Exist(FX_WSTR fileName);
 FX_BOOL         FX_File_Delete(FX_BSTR fileName);
 FX_BOOL         FX_File_Delete(FX_WSTR fileName);
 FX_BOOL         FX_File_Copy(FX_BSTR fileNameSrc, FX_BSTR fileNameDst);
 FX_BOOL         FX_File_Copy(FX_WSTR fileNameSrc, FX_WSTR fileNameDst);
 FX_BOOL         FX_File_Move(FX_BSTR fileNameSrc, FX_BSTR fileNameDst);
 FX_BOOL         FX_File_Move(FX_WSTR fileNameSrc, FX_WSTR fileNameDst);
 class IFX_StreamWrite
 {
 public:
-
+    virtual ~IFX_StreamWrite() { }
     virtual void                Release() = 0;
 
     virtual     FX_BOOL         WriteBlock(const void* pData, size_t size) = 0;
 };
 class IFX_FileWrite : public IFX_StreamWrite
 {
 public:
 
     virtual void                        Release() = 0;
 
     virtual FX_FILESIZE         GetSize() = 0;
 
     virtual FX_BOOL                     Flush() = 0;
 
     virtual     FX_BOOL                 WriteBlock(const void* pData, FX_FILESIZE offset, size_t size) = 0;
     virtual     FX_BOOL                 WriteBlock(const void* pData, size_t size)
     {
         return WriteBlock(pData, GetSize(), size);
     }
 };
 IFX_FileWrite* FX_CreateFileWrite(FX_LPCSTR filename);
 IFX_FileWrite* FX_CreateFileWrite(FX_LPCWSTR filename);
 class IFX_StreamRead
 {
 public:
+    virtual ~IFX_StreamRead() { }
 
     virtual void                        Release() = 0;
 
     virtual FX_BOOL                     IsEOF() = 0;
 
     virtual FX_FILESIZE         GetPosition() = 0;
 
     virtual size_t                      ReadBlock(void* buffer, size_t size) = 0;
 };
 class IFX_FileRead : IFX_StreamRead
 {
 public:
-
     virtual void                        Release() = 0;
 
     virtual FX_FILESIZE         GetSize() = 0;
 
     virtual FX_BOOL                     IsEOF()
     {
         return FALSE;
     }
 
     virtual FX_FILESIZE         GetPosition()
@@ skipping 75 matching lines @@
 
     virtual FX_BOOL                     ReadNextBlock(FX_BOOL bRestart = FALSE) = 0;
 
     virtual FX_LPCBYTE          GetBlockBuffer() = 0;
 
     virtual size_t                      GetBlockSize() = 0;
 
     virtual FX_FILESIZE         GetBlockOffset() = 0;
 };
 #endif