Switch WindowedNotificationObserver to use base::RunLoop.

extensions/test/extension_test_notification_observer.cc

 // Copyright 2016 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.
 
 #include "extensions/test/extension_test_notification_observer.h"
 
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/notification_service.h"
@@ skipping 122 matching lines @@
 void ExtensionTestNotificationObserver::Watch(
     int type,
     const content::NotificationSource& source) {
   CHECK(!observer_);
   observer_.reset(new content::WindowedNotificationObserver(type, source));
   registrar_.Add(this, type, source);
 }
 
 void ExtensionTestNotificationObserver::Wait() {
   observer_->Wait();
+  // TODO(...): Find out why tests fail without it.
+  content::RunAllPendingInMessageLoop();
 
   registrar_.RemoveAll();
   observer_.reset();
 }
 
 void ExtensionTestNotificationObserver::Observe(
     int type,
     const content::NotificationSource& source,
     const content::NotificationDetails& details) {
   switch (type) {
@@ skipping 48 matching lines @@
   condition_.Reset();
   quit_closure_.Reset();
 }
 
 void ExtensionTestNotificationObserver::MaybeQuit() {
   if (condition_.Run())
     quit_closure_.Run();
 }
 
 }  // namespace extensions