Send certificate errors from worker fetch context for off-main-thread-fetch.

chrome/test/data/ssl/unsafe_fetching_worker.js

Index: chrome/test/data/ssl/unsafe_fetching_worker.js
diff --git a/chrome/test/data/ssl/unsafe_fetching_worker.js b/chrome/test/data/ssl/unsafe_fetching_worker.js
new file mode 100644
index 0000000000000000000000000000000000000000..36589840ee1da5565c1842a29cbaacbb6be2e6a4
--- /dev/null
+++ b/chrome/test/data/ssl/unsafe_fetching_worker.js
@@ -0,0 +1,5 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+fetch("REPLACE_WITH_TEST_FILE_URL", {mode: 'no-cors'})
+  .then(_ => postMessage("loaded"), _ => postMessage("failed"));