Implement the events for Background Fetch

third_party/WebKit/LayoutTests/http/tests/background_fetch/resources/background-fetch-event-worker.js

+'use strict';
+
+importScripts('/resources/testharness.js');
+
+test(function() {
+  assert_own_property(self, 'BackgroundFetchEvent');
+
+  // The `tag` is required in the BackgroundFetchEventInit.
+  assert_throws(null, () => new BackgroundFetchEvent('BackgroundFetchEvent'));
+  assert_throws(null, () => new BackgroundFetchEvent('BackgroundFetchEvent', {}));
+
+  const event = new BackgroundFetchEvent('BackgroundFetchEvent', {
+    tag: 'my-tag'
+  });
+
+  assert_equals(event.type, 'BackgroundFetchEvent');
+  assert_equals(event.cancelable, false);
+  assert_equals(event.bubbles, false);
+  assert_equals(event.tag, 'my-tag');
+
+  assert_inherits(event, 'waitUntil');
+
+}, 'Verifies that the BackgroundFetchEvent can be constructed.');