Add virtual destructors for the Pepper API thunks.

ppapi/thunk/ppb_url_loader_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_LOADER_API_H_
 #define PPAPI_THUNK_URL_LOADER_API_H_
 
 #include "ppapi/c/ppb_url_loader.h"
 #include "ppapi/c/trusted/ppb_url_loader_trusted.h"
 
 namespace ppapi {
 namespace thunk {
 
 class PPB_URLLoader_API {
  public:
+  virtual ~PPB_URLLoader_API() {}
+
   virtual int32_t Open(PP_Resource request_id,
                        PP_CompletionCallback callback) = 0;
   virtual int32_t FollowRedirect(PP_CompletionCallback callback) = 0;
   virtual PP_Bool GetUploadProgress(int64_t* bytes_sent,
                                     int64_t* total_bytes_to_be_sent) = 0;
   virtual PP_Bool GetDownloadProgress(int64_t* bytes_received,
                                       int64_t* total_bytes_to_be_received) = 0;
   virtual PP_Resource GetResponseInfo() = 0;
   virtual int32_t ReadResponseBody(void* buffer,
                                    int32_t bytes_to_read,
                                    PP_CompletionCallback callback) = 0;
   virtual int32_t FinishStreamingToFile(PP_CompletionCallback callback) = 0;
   virtual void Close() = 0;
 
   // Trusted API.
   virtual void GrantUniversalAccess() = 0;
   virtual void SetStatusCallback(PP_URLLoaderTrusted_StatusCallback cb) = 0;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_URL_LOADER_API_H_