Fix typo in notification_launch_id.h

Change-Id: I45bd5319c04220ea2bd9ceb5dbb5568ad9e1b241
Reviewed-on: https://chromium-review.googlesource.com/973896
Commit-Queue: Peter Beverloo <peter@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544848}

chrome/browser/notifications/notification_launch_id.h

@@ -90,7 +90,7 @@ class NotificationLaunchId {
   // The profile id this launch ID is associated with. The string is UTF8.
   std::string profile_id_;
 
-  // A flat indicating if the notification associated with this launch ID is in
+  // A flag indicating if the notification associated with this launch ID is in
   // incognito mode or not.
   bool incognito_ = false;