Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/download/save_file_resource_handler.cc

Index: content/browser/download/save_file_resource_handler.cc
diff --git a/content/browser/download/save_file_resource_handler.cc b/content/browser/download/save_file_resource_handler.cc
index efea74fb3cc556345c2207a21ab2d72660f154de..98b332de01c3998bdf7fa2aa7a9db292cdcc87b7 100644
--- a/content/browser/download/save_file_resource_handler.cc
+++ b/content/browser/download/save_file_resource_handler.cc
@@ -70,8 +70,10 @@ void SaveFileResourceHandler::OnWillStart(
   }
 }
 
-bool SaveFileResourceHandler::OnWillRead(scoped_refptr<net::IOBuffer>* buf,
-                                         int* buf_size) {
+void SaveFileResourceHandler::OnWillRead(
+    scoped_refptr<net::IOBuffer>* buf,
+    int* buf_size,
+    std::unique_ptr<ResourceController> controller) {
   DCHECK_EQ(AuthorizationState::AUTHORIZED, authorization_state_);
   DCHECK(buf && buf_size);
   if (!read_buffer_.get()) {
@@ -79,7 +81,7 @@ bool SaveFileResourceHandler::OnWillRead(scoped_refptr<net::IOBuffer>* buf,
     read_buffer_ = new net::IOBuffer(*buf_size);
   }
   *buf = read_buffer_.get();
-  return true;
+  controller->Resume();
 }
 
 void SaveFileResourceHandler::OnReadCompleted(