[Extensions] Enable ServiceWorkerLazyBackgroundTest.EventsAfterRestart.

The root cause is fixed by
https://crrev.com/b8e24bdbf6bbe43bc32fd684f2a0aad914e804d2
and the test doesn't flake locally or on trybots anymore.

Bug: 834200
Change-Id: I0bca3a12374cb70554c73063d7913dfbeec78e07
Reviewed-on: https://chromium-review.googlesource.com/1225700Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591203}

chrome/browser/extensions/service_worker_apitest.cc

@@ -1058,9 +1058,7 @@ IN_PROC_BROWSER_TEST_P(ServiceWorkerLazyBackgroundTest,
   lazy_observer.Wait();
 }
 
-// Flaky: http://crbug/834200.
-IN_PROC_BROWSER_TEST_P(ServiceWorkerLazyBackgroundTest,
-                       DISABLED_EventsAfterRestart) {
+IN_PROC_BROWSER_TEST_P(ServiceWorkerLazyBackgroundTest, EventsAfterRestart) {
   ExtensionTestMessageListener newtab_listener("hello-newtab", false);
   content::WebContents* new_web_contents =
       AddTab(browser(), GURL(url::kAboutBlankURL));