Make GetDisplayedNotifications asynchronous.

chrome/browser/notifications/notification_platform_bridge_mac.mm

Index: chrome/browser/notifications/notification_platform_bridge_mac.mm
diff --git a/chrome/browser/notifications/notification_platform_bridge_mac.mm b/chrome/browser/notifications/notification_platform_bridge_mac.mm
index 29277e13da0fd4a6712a8d6530ad8a0a15d2c625..249a9794ad29e0f125744cf425109cf57104e0aa 100644
--- a/chrome/browser/notifications/notification_platform_bridge_mac.mm
+++ b/chrome/browser/notifications/notification_platform_bridge_mac.mm
@@ -273,23 +273,25 @@ void NotificationPlatformBridgeMac::Close(const std::string& profile_id,
 #endif  // ENABLE_XPC_NOTIFICATIONS
 }
 
-bool NotificationPlatformBridgeMac::GetDisplayed(
+void NotificationPlatformBridgeMac::GetDisplayed(
     const std::string& profile_id,
     bool incognito,
-    std::set<std::string>* notifications) const {
-  DCHECK(notifications);
-
+    const DisplayedNotificationsCallback& callback) const {
+  auto displayed_notifications = base::MakeUnique<std::set<std::string>>();
   NSString* current_profile_id = base::SysUTF8ToNSString(profile_id);
   for (NSUserNotification* toast in
        [notification_center_ deliveredNotifications]) {
     NSString* toast_profile_id = [toast.userInfo
         objectForKey:notification_constants::kNotificationProfileId];
     if ([toast_profile_id isEqualToString:current_profile_id]) {
-      notifications->insert(base::SysNSStringToUTF8([toast.userInfo
+      displayed_notifications->insert(base::SysNSStringToUTF8([toast.userInfo
           objectForKey:notification_constants::kNotificationId]));
     }
   }
-  return true;
+  content::BrowserThread::PostTask(
+      content::BrowserThread::UI, FROM_HERE,
+      base::Bind(callback, base::Passed(&displayed_notifications),
+                 true /* supports sync */));
 }
 
 // static