Make SimpleURLLoader only have one redirect callback

Nothing seems to depend on the possibility of having multiple callbacks.

Change-Id: I9935be6345d37fe9d445f741c803aab949aab125
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1930096
Auto-Submit: Jeremy Apthorp <jeremya@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Jeremy Apthorp <jeremya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718721}

services/network/public/cpp/simple_url_loader.cc

@@ -333,7 +333,7 @@ class SimpleURLLoaderImpl : public SimpleURLLoader,
   // closed.
   void MaybeComplete();
 
-  std::vector<OnRedirectCallback> on_redirect_callback_;
+  OnRedirectCallback on_redirect_callback_;
   OnResponseStartedCallback on_response_started_callback_;
   UploadProgressCallback on_upload_progress_callback_;
   DownloadProgressCallback on_download_progress_callback_;
@@ -1242,8 +1242,7 @@ void SimpleURLLoaderImpl::SetOnRedirectCallback(
   // Check if a request has not yet been started.
   DCHECK(!body_handler_);
 
-  on_redirect_callback_.push_back(on_redirect_callback);
-  DCHECK(on_redirect_callback);
+  on_redirect_callback_ = on_redirect_callback;
 }
 
 void SimpleURLLoaderImpl::SetOnResponseStartedCallback(
@@ -1607,16 +1606,14 @@ void SimpleURLLoaderImpl::OnReceiveRedirect(
   }
 
   std::vector<std::string> removed_headers;
-  for (auto callback : on_redirect_callback_) {
-    if (callback) {
+  if (on_redirect_callback_) {
     base::WeakPtr<SimpleURLLoaderImpl> weak_this =
         weak_ptr_factory_.GetWeakPtr();
-      callback.Run(redirect_info, *response_head, &removed_headers);
+    on_redirect_callback_.Run(redirect_info, *response_head, &removed_headers);
     // If deleted by the callback, bail now.
     if (!weak_this)
       return;
   }
-  }
 
   final_url_ = redirect_info.new_url;
   url_loader_->FollowRedirect(removed_headers, {} /* modified_headers */,