Add virtual destructors for the Pepper API thunks.

ppapi/thunk/ppb_url_request_info_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_URL_REQUEST_INFO_API_H_
 #define PPAPI_THUNK_URL_REQUEST_INFO_API_H_
 
 #include "ppapi/c/ppb_url_request_info.h"
 
 namespace ppapi {
 namespace thunk {
 
 class PPB_URLRequestInfo_API {
  public:
+  virtual ~PPB_URLRequestInfo_API() {}
+
   virtual PP_Bool SetProperty(PP_URLRequestProperty property,
                               PP_Var var) = 0;
   virtual PP_Bool AppendDataToBody(const void* data, uint32_t len) = 0;
   virtual PP_Bool AppendFileToBody(PP_Resource file_ref,
                                    int64_t start_offset,
                                    int64_t number_of_bytes,
                                    PP_Time expected_last_modified_time) = 0;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_URL_REQUEST_INFO_API_H_