Add virtual destructors for the Pepper API thunks.

ppapi/thunk/ppb_font_api.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_THUNK_PPB_FONT_API_H_
 #define PPAPI_THUNK_PPB_FONT_API_H_
 
 #include "ppapi/c/dev/ppb_font_dev.h"
 #include "ppapi/proxy/interface_id.h"
 
 namespace ppapi {
 namespace thunk {
 
 // API for static font functions.
 class PPB_Font_FunctionAPI {
  public:
+  virtual ~PPB_Font_FunctionAPI() {}
+
+  virtual PP_Var GetFontFamilies(PP_Instance instance) = 0;
+
   static const ::pp::proxy::InterfaceID interface_id =
       ::pp::proxy::INTERFACE_ID_PPB_FONT;
-
-  virtual PP_Var GetFontFamilies(PP_Instance instance) = 0;
 };
 
 // API for font resources.
 class PPB_Font_API {
  public:
+  virtual ~PPB_Font_API() {}
+
   virtual PP_Bool Describe(PP_FontDescription_Dev* description,
                            PP_FontMetrics_Dev* metrics) = 0;
   virtual PP_Bool DrawTextAt(PP_Resource image_data,
                              const PP_TextRun_Dev* text,
                              const PP_Point* position,
                              uint32_t color,
                              const PP_Rect* clip,
                              PP_Bool image_data_is_opaque) = 0;
   virtual int32_t MeasureText(const PP_TextRun_Dev* text) = 0;
   virtual uint32_t CharacterOffsetForPixel(const PP_TextRun_Dev* text,
                                            int32_t pixel_position) = 0;
   virtual int32_t PixelOffsetForCharacter(const PP_TextRun_Dev* text,
                                           uint32_t char_offset) = 0;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_PPB_FONT_API_H_