PPAPI: Force async callback invocation option.

ppapi/cpp/url_loader.h

 // Copyright (c) 2010 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_CPP_URL_LOADER_H_
 #define PPAPI_CPP_URL_LOADER_H_
 
 #include "ppapi/c/pp_stdint.h"
 #include "ppapi/cpp/resource.h"
 
@@ skipping 16 matching lines @@
 //           did_open_(false) {
 //     }
 //     void ProcessURL(const char* url) {
 //       CompletionCallback* cc = NewCallback();
 //       int32_t rv = loader_.Open(MakeRequest(url), cc);
 //       if (rv != PP_Error_WouldBlock)
 //         cc->Run(rv);
 //     }
 //    private:
 //     CompletionCallback* NewCallback() {
-//       return factory_.NewCallback(&MyHandler::DidCompleteIO);
+//       return factory_.NewOptionalCallback(&MyHandler::DidCompleteIO);
 //     }
 //     URLRequestInfo MakeRequest(const char* url) {
 //       URLRequestInfo request;
 //       request.SetURL(url);
 //       request.SetMethod("GET");
 //       request.SetFollowRedirects(true);
 //       return request;
 //     }
 //     void DidCompleteIO(int32_t result) {
 //       if (result > 0) {
@@ skipping 52 matching lines @@
   int32_t ReadResponseBody(void* buffer,
                            int32_t bytes_to_read,
                            const CompletionCallback& cc);
   int32_t FinishStreamingToFile(const CompletionCallback& cc);
   void Close();
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_URL_LOADER_H_