Switch WindowedNotificationObserver to use base::RunLoop.

extensions/test/extension_test_notification_observer.cc

Index: extensions/test/extension_test_notification_observer.cc
diff --git a/extensions/test/extension_test_notification_observer.cc b/extensions/test/extension_test_notification_observer.cc
index 0e4d75d0ccdcbfa8cfe6e07dfb27c4b3ab52ef06..8c79ac54cbebde1de7c8146d42116ce31c5e3375 100644
--- a/extensions/test/extension_test_notification_observer.cc
+++ b/extensions/test/extension_test_notification_observer.cc
@@ -141,6 +141,9 @@ void ExtensionTestNotificationObserver::Watch(
 void ExtensionTestNotificationObserver::Wait() {
   observer_->Wait();
 
+  // TODO(https://crbug.com/695073): Find out why tests fail without it.
+  content::RunAllPendingInMessageLoop();
+
   registrar_.RemoveAll();
   observer_.reset();
 }
@@ -187,16 +190,15 @@ void ExtensionTestNotificationObserver::WaitForCondition(
     return;
   condition_ = condition;
 
-  scoped_refptr<content::MessageLoopRunner> runner(
-      new content::MessageLoopRunner);
-  quit_closure_ = runner->QuitClosure();
+  base::RunLoop run_loop;
+  quit_closure_ = run_loop.QuitClosure();
 
   std::unique_ptr<base::CallbackList<void()>::Subscription> subscription;
   if (notification_set) {
     subscription = notification_set->callback_list().Add(base::Bind(
         &ExtensionTestNotificationObserver::MaybeQuit, base::Unretained(this)));
   }
-  runner->Run();
+  run_loop.Run();
 
   condition_.Reset();
   quit_closure_.Reset();