Fix -Wnon-virtual-dtor compiler warnings.

core/include/fxcodec/fx_codec_provider.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_CODEC_PROVIDER_H_
 #define _FX_CODEC_PROVIDER_H_
 class IFX_JpegProvider
 {
 public:
-
     virtual void                Release() = 0;
 
     virtual void*               CreateDecoder(FX_LPCBYTE src_buf, FX_DWORD src_size, int width, int height, int nComps, FX_BOOL ColorTransform) = 0;
 
 
     virtual void                DestroyDecoder(void* pDecoder) = 0;
 
     virtual void                DownScale(void* pDecoder, int dest_width, int dest_height) = 0;
 
     virtual FX_BOOL             Rewind(void* pDecoder) = 0;
@@ skipping 19 matching lines @@
     virtual int                 ReadHeader(void* pContext, int* width, int* height, int* nComps) = 0;
 
 
     virtual int                 StartScanline(void* pContext, int down_scale) = 0;
 
 
     virtual FX_BOOL             ReadScanline(void* pContext, FX_LPBYTE dest_buf) = 0;
 
 
     virtual FX_DWORD    GetAvailInput(void* pContext, FX_LPBYTE* avail_buf_ptr = NULL) = 0;
+
+protected:
+    ~IFX_JpegProvider() { }
 };
 #endif