Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/download/download_resource_handler.cc

Index: content/browser/download/download_resource_handler.cc
diff --git a/content/browser/download/download_resource_handler.cc b/content/browser/download/download_resource_handler.cc
index e52984a1c478b7c3063c95a0768208a4bc59dca2..c7ba502b98387a62fd9a9a69b3853101763d5c00 100644
--- a/content/browser/download/download_resource_handler.cc
+++ b/content/browser/download/download_resource_handler.cc
@@ -171,9 +171,16 @@ void DownloadResourceHandler::OnWillStart(
 
 // Create a new buffer, which will be handed to the download thread for file
 // writing and deletion.
-bool DownloadResourceHandler::OnWillRead(scoped_refptr<net::IOBuffer>* buf,
-                                         int* buf_size) {
-  return core_.OnWillRead(buf, buf_size);
+void DownloadResourceHandler::OnWillRead(
+    scoped_refptr<net::IOBuffer>* buf,
+    int* buf_size,
+    std::unique_ptr<ResourceController> controller) {
+  if (!core_.OnWillRead(buf, buf_size)) {
+    controller->Cancel();
+    return;
+  }
+
+  controller->Resume();
 }
 
 // Pass the buffer to the download file writer.