Support add/overwrite redirect request headers in NavigationURLLoader

https://chromium-review.googlesource.com/c/chromium/src/+/1072643

atom/browser/net/atom_url_request.cc

@@ -267,7 +267,8 @@ void AtomURLRequest::DoCancel() {
 void AtomURLRequest::DoFollowRedirect() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   if (request_ && request_->is_redirecting() && redirect_policy_ == "manual") {
-    request_->FollowDeferredRedirect();
+    request_->FollowDeferredRedirect(
+        base::nullopt /* modified_request_headers */);
   }
 }