Extract Notifications kClickWasNotAnAction constant

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 82cc07df3232a4b5e2a970097cee7f626ae50777..a5b57892faacd82b67b97c08e7ccea17fb0990f0 100644
--- a/content/shell/browser/layout_test/layout_test_notification_manager.cc
+++ b/content/shell/browser/layout_test/layout_test_notification_manager.cc
@@ -113,8 +113,10 @@ void LayoutTestNotificationManager::SimulateClick(const std::string& title,
   // First check for page-notifications with the given title.
   const auto& page_iterator = page_notifications_.find(title);
   if (page_iterator != page_notifications_.end()) {
-    DCHECK_EQ(action_index, -1) << "Action buttons are only supported for "
-                                   "persistent notifications";
+    DCHECK_EQ(action_index,
+              kNotificationClickWasNotAnAction) << "Action buttons are only "
+                                                   "supported for persistent "
+                                                   "notifications";
     page_iterator->second->NotificationClick();
     return;
   }