Minor clickNotificationButton command code re-org

Minor clickNotificationButton re-org while I was running my ruler over
this code. No change in behavior, no new tests.

Tbr: slangley
Bug: 833834
Change-Id: Ic23e13e89ab0d3a30d17d456c6c12c781fbc02f4
Reviewed-on: https://chromium-review.googlesource.com/1041368
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Stuart Langley <slangley@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555893}

chrome/browser/chromeos/file_manager/file_manager_browsertest_base.cc

@@ -754,17 +754,16 @@ void FileManagerBrowserTestBase::OnCommand(const std::string& name,
   if (name == "clickNotificationButton") {
     std::string extension_id;
     std::string notification_id;
-    int index;
     ASSERT_TRUE(value.GetString("extensionId", &extension_id));
     ASSERT_TRUE(value.GetString("notificationId", &notification_id));
-    ASSERT_TRUE(value.GetInteger("index", &index));
-
-    const std::string delegate_id = extension_id + "-" + notification_id;
 
+    const auto delegate_id = extension_id + "-" + notification_id;
     base::Optional<message_center::Notification> notification =
         display_service_->GetNotification(delegate_id);
     EXPECT_TRUE(notification);
 
+    int index;
+    ASSERT_TRUE(value.GetInteger("index", &index));
     display_service_->SimulateClick(NotificationHandler::Type::EXTENSION,
                                     delegate_id, index, base::nullopt);
     return;