Revert: Prevent promise reject to be sync scheduled during DocumentLoader detach

Bug: 868592
Change-Id: Ida5a487e26634b5f424e82a0323acfab939ffe84
Reviewed-on: https://chromium-review.googlesource.com/1164149Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581142}

third_party/blink/renderer/core/fetch/fetch_manager.cc

@@ -901,12 +901,6 @@ void FetchManager::Loader::Failed(const String& message) {
         ConsoleMessage::Create(kJSMessageSource, kErrorMessageLevel, message));
   }
   if (resolver_) {
-    // This ScriptForbiddenScope forcibly punt the reject task to prevent the
-    // promise reject microtask to be queued synchronously during
-    // DocumentLoader detach.
-    // TODO(crbug.com/868592) Fix this properly.
-    ScriptForbiddenScope forbid;
-
     ScriptState* state = resolver_->GetScriptState();
     ScriptState::Scope scope(state);
     resolver_->Reject(V8ThrowException::CreateTypeError(state->GetIsolate(),