Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/download/save_file_resource_handler.h

Index: content/browser/download/save_file_resource_handler.h
diff --git a/content/browser/download/save_file_resource_handler.h b/content/browser/download/save_file_resource_handler.h
index 63f061d7b19f27f2a068dfdd87186c090e083110..334837bc9fa6b3bc922e14363a5f23611f0cd869 100644
--- a/content/browser/download/save_file_resource_handler.h
+++ b/content/browser/download/save_file_resource_handler.h
@@ -67,8 +67,9 @@ class SaveFileResourceHandler : public ResourceHandler {
 
   // 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,