OOR-CORS: fix to finalize preflight request on some errors

Current code does not finalize preflight requests correctly when
the preflight request failed without receiving HTTP response headers.

Bug: 803766
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I1c91e3ecf76fdb368e3d55256885f52edf6fcbb3
Reviewed-on: https://chromium-review.googlesource.com/1027556
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554643}

services/network/cors/preflight_controller.cc

@@ -301,11 +301,12 @@ class PreflightController::PreflightLoader final {
   }
 
   void HandleResponseBody(std::unique_ptr<std::string> response_body) {
-    // Reached only when the request fails without receiving headers.
+    // Reached only when the request fails without receiving headers, e.g.
+    // unknown hosts, unreachable remote, reset by peer, and so on.
+    // See https://crbug.com/826868 for related discussion.
     DCHECK(!response_body);
-
-    // TODO(toyoshim): FinalizeLoader() and RemoveFromController() need to be
-    // called in this case. Try in the follow-up change.
+    FinalizeLoader();
+    RemoveFromController();
   }
 
   void FinalizeLoader() {