Add virtual destructors for the Pepper API thunks.

ppapi/thunk/ppb_video_layer_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_VIDEO_LAYER_API_H_
 #define PPAPI_THUNK_VIDEO_LAYER_API_H_
 
 #include "ppapi/c/dev/ppb_video_layer_dev.h"
 
 namespace ppapi {
 namespace thunk {
 
 class PPB_VideoLayer_API {
  public:
+  virtual ~PPB_VideoLayer_API() {}
+
   virtual void SetPixelFormat(PP_VideoLayerPixelFormat_Dev pixel_format) = 0;
   virtual void SetNativeSize(const PP_Size* size) = 0;
   virtual void SetClipRect(const PP_Rect* clip_rect) = 0;
   virtual PP_Bool IsReady() = 0;
   virtual PP_Bool UpdateContent(uint32_t no_of_planes, const void** planes) = 0;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_VIDEO_LAYER_API_H_