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

chrome/test/data/ssl/unsafe_importing_worker.js

Index: chrome/test/data/ssl/unsafe_importing_worker.js
diff --git a/chrome/test/data/ssl/unsafe_importing_worker.js b/chrome/test/data/ssl/unsafe_importing_worker.js
new file mode 100644
index 0000000000000000000000000000000000000000..3423ab300e4d93310793f4d1b24926798e448986
--- /dev/null
+++ b/chrome/test/data/ssl/unsafe_importing_worker.js
@@ -0,0 +1,9 @@
+// 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.
+var message = "failed";
+try {
+  importScripts("REPLACE_WITH_IMPORTED_JS_URL");
+} catch(ex) {
+}
+postMessage(message);