Drop the const modifier on NotificationDisplayService::GetDisplayed

chrome/browser/notifications/stub_notification_display_service.cc

Index: chrome/browser/notifications/stub_notification_display_service.cc
diff --git a/chrome/browser/notifications/stub_notification_display_service.cc b/chrome/browser/notifications/stub_notification_display_service.cc
index 981d47206592fbfc2a84a7e91485343417f2da35..d8a8a10c86724863f34aad57dd4b737518721480 100644
--- a/chrome/browser/notifications/stub_notification_display_service.cc
+++ b/chrome/browser/notifications/stub_notification_display_service.cc
@@ -78,7 +78,7 @@ void StubNotificationDisplayService::Close(
 }
 
 void StubNotificationDisplayService::GetDisplayed(
-    const DisplayedNotificationsCallback& callback) const {
+    const DisplayedNotificationsCallback& callback) {
   std::unique_ptr<std::set<std::string>> notifications =
       base::MakeUnique<std::set<std::string>>();