Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/download/download_resource_handler.h

Index: content/browser/download/download_resource_handler.h
diff --git a/content/browser/download/download_resource_handler.h b/content/browser/download/download_resource_handler.h
index 0847f75e8077da03de6404f1684acc50c86e14b2..ad2b38e3a18dbda48d0ccaf0d806477009f4ca6a 100644
--- a/content/browser/download/download_resource_handler.h
+++ b/content/browser/download/download_resource_handler.h
@@ -66,8 +66,9 @@ class CONTENT_EXPORT DownloadResourceHandler
 
   // Create 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;
 
   void OnReadCompleted(int bytes_read,
                        std::unique_ptr<ResourceController> controller) override;