Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/download/save_file_resource_handler.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_DOWNLOAD_SAVE_FILE_RESOURCE_HANDLER_H_
 #define CONTENT_BROWSER_DOWNLOAD_SAVE_FILE_RESOURCE_HANDLER_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 49 matching lines @@
   void OnResponseStarted(
       ResourceResponse* response,
       std::unique_ptr<ResourceController> controller) override;
 
   // Pass-through implementation.
   void OnWillStart(const GURL& url,
                    std::unique_ptr<ResourceController> controller) override;
 
   // Creates a new buffer, which will be handed to the download thread for file
   // writing and deletion.
-  bool OnWillRead(scoped_refptr<net::IOBuffer>* buf,
-                  int* buf_size) override;
+  void OnWillRead(scoped_refptr<net::IOBuffer>* buf,
+                  int* buf_size,
+                  std::unique_ptr<ResourceController> controller) override;
 
   // Passes the buffer to the download file writer.
   void OnReadCompleted(int bytes_read,
                        std::unique_ptr<ResourceController> controller) override;
 
   void OnResponseCompleted(
       const net::URLRequestStatus& status,
       std::unique_ptr<ResourceController> controller) override;
 
   // N/A to this flavor of SaveFileResourceHandler.
@@ skipping 23 matching lines @@
   AuthorizationState authorization_state_;
 
   static const int kReadBufSize = 32768;  // bytes
 
   DISALLOW_COPY_AND_ASSIGN(SaveFileResourceHandler);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_SAVE_FILE_RESOURCE_HANDLER_H_