Make GetDisplayedNotifications asynchronous.

content/shell/browser/layout_test/layout_test_notification_manager.cc

Index: content/shell/browser/layout_test/layout_test_notification_manager.cc
diff --git a/content/shell/browser/layout_test/layout_test_notification_manager.cc b/content/shell/browser/layout_test/layout_test_notification_manager.cc
index cfac368b75d264ebd9f7f0608687652ad95e0180..8f798a013e70216efe0300b0f53a78a576366a5d 100644
--- a/content/shell/browser/layout_test/layout_test_notification_manager.cc
+++ b/content/shell/browser/layout_test/layout_test_notification_manager.cc
@@ -83,14 +83,15 @@ void LayoutTestNotificationManager::ClosePersistentNotification(
   persistent_notifications_.erase(notification_id);
 }
 
-bool LayoutTestNotificationManager::GetDisplayedNotifications(
+void LayoutTestNotificationManager::GetDisplayedNotifications(
     BrowserContext* browser_context,
-    std::set<std::string>* displayed_notifications) {
-  DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  DCHECK(displayed_notifications);
-
-  // Notifications will never outlive the lifetime of running layout tests.
-  return false;
+    const NotificationResultCallback& callback) {
+  std::unique_ptr<std::set<std::string>> displayedNotifications =

[Peter Beverloo, 2017/03/15 18:07:51]

nit: displayed_notifications

[Miguel Garcia, 2017/03/16 14:57:43]

Done.

+      base::MakeUnique<std::set<std::string>>();
+  content::BrowserThread::PostTask(
+      content::BrowserThread::UI, FROM_HERE,

[Peter Beverloo, 2017/03/15 18:07:51]

nit: drop content:: from these, you are in that namespace

[Miguel Garcia, 2017/03/16 14:57:42]

Done.

+      base::Bind(callback, base::Passed(&displayedNotifications),
+                 false /* supports getting displayed notifications */));
 }
 
 void LayoutTestNotificationManager::SimulateClick(