Add virtual destructors for the Pepper API thunks.

ppapi/thunk/ppb_instance_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_INSTANCE_API_H_
 #define PPAPI_THUNK_INSTANCE_API_H_
 
 #include "ppapi/c/ppb_instance.h"
 #include "ppapi/c/pp_bool.h"
 #include "ppapi/c/pp_size.h"
 #include "ppapi/c/private/ppb_instance_private.h"
 #include "ppapi/proxy/interface_id.h"
 
 namespace ppapi {
 namespace thunk {
 
 class PPB_Instance_FunctionAPI {
  public:
-  static const ::pp::proxy::InterfaceID interface_id =
-      ::pp::proxy::INTERFACE_ID_PPB_INSTANCE;
+  virtual ~PPB_Instance_FunctionAPI() {}
 
   virtual PP_Bool BindGraphics(PP_Instance instance, PP_Resource device) = 0;
   virtual PP_Bool IsFullFrame(PP_Instance instance) = 0;
 
   // InstancePrivate.
   virtual PP_Var GetWindowObject(PP_Instance instance) = 0;
   virtual PP_Var GetOwnerElementObject(PP_Instance instance) = 0;
   virtual PP_Var ExecuteScript(PP_Instance instance,
                                PP_Var script,
                                PP_Var* exception) = 0;
 
   // Fullscreen.
   virtual PP_Bool IsFullscreen(PP_Instance instance) = 0;
   virtual PP_Bool SetFullscreen(PP_Instance instance, PP_Bool fullscreen) = 0;
   virtual PP_Bool GetScreenSize(PP_Instance instance, PP_Size* size) = 0;
+
+  static const ::pp::proxy::InterfaceID interface_id =
+      ::pp::proxy::INTERFACE_ID_PPB_INSTANCE;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_INSTANCE_API_H_