Import w3c tests for the service workers

third_party/WebKit/LayoutTests/imported/wpt/service-workers/service-worker/resources/install-event-type-worker.js

 importScripts('worker-testharness.js');
 
 self.oninstall = function(event) {
     assert_true(event instanceof ExtendableEvent);
-    assert_true(event instanceof InstallEvent);
     assert_equals(event.type, 'install');
     assert_false(event.cancelable);
     assert_false(event.bubbles);
 };