Make GetDisplayedNotifications asynchronous.

chrome/browser/notifications/platform_notification_service_impl.cc

Index: chrome/browser/notifications/platform_notification_service_impl.cc
diff --git a/chrome/browser/notifications/platform_notification_service_impl.cc b/chrome/browser/notifications/platform_notification_service_impl.cc
index 6c70a2ced43d75a2728f84068b6f68685dfc4d7c..36c7cb4afc9c1903ba7c660703cdac5c8f6b007b 100644
--- a/chrome/browser/notifications/platform_notification_service_impl.cc
+++ b/chrome/browser/notifications/platform_notification_service_impl.cc
@@ -379,18 +379,23 @@ void PlatformNotificationServiceImpl::ClosePersistentNotification(
                                                 notification_id);
 }
 
-bool PlatformNotificationServiceImpl::GetDisplayedNotifications(
+void PlatformNotificationServiceImpl::GetDisplayedNotifications(
     BrowserContext* browser_context,
-    std::set<std::string>* displayed_notifications) {
-  DCHECK(displayed_notifications);
+    const NotificationResultCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   Profile* profile = Profile::FromBrowserContext(browser_context);
-  if (!profile || profile->AsTestingProfile())
-    return false;  // Tests will not have a message center.
-
-  return GetNotificationDisplayService(profile)->GetDisplayed(
-      displayed_notifications);
+  // Tests will not have a message center.
+  if (!profile || profile->AsTestingProfile()) {
+    std::unique_ptr<std::set<std::string>> displayedNotifications =

[Peter Beverloo, 2017/03/15 18:07:50]

displayed_notifications or delete per the comment on the
PlatformNotificationService interface

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

Done.

+        base::MakeUnique<std::set<std::string>>();
+    content::BrowserThread::PostTask(
+        content::BrowserThread::UI, FROM_HERE,
+        base::Bind(callback, base::Passed(&displayedNotifications),
+                   false /* supports getting displayed notifications */));

[Peter Beverloo, 2017/03/15 18:07:50]

I'd just take the easy path here and use:

  callback.Run(std::move(displayed_notifications), false /* supported */);

You are on the UI thread, and there's only a single user of the //content API.

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

Done.

+    return;
+  }
+  GetNotificationDisplayService(profile)->GetDisplayed(callback);
 }
 
 void PlatformNotificationServiceImpl::OnClickEventDispatchComplete(