[NTP::SectionOrder] Replace CategoryFactory with a category ranker.

components/ntp_snippets/category_rankers/mock_category_ranker.cc

Index: components/ntp_snippets/category_rankers/mock_category_ranker.cc
diff --git a/components/ntp_snippets/category_rankers/mock_category_ranker.cc b/components/ntp_snippets/category_rankers/mock_category_ranker.cc
new file mode 100644
index 0000000000000000000000000000000000000000..dc9e9f70a56ca56b91c75bef7ded9f0b4676f38d
--- /dev/null
+++ b/components/ntp_snippets/category_rankers/mock_category_ranker.cc
@@ -0,0 +1,13 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/ntp_snippets/category_rankers/mock_category_ranker.h"
+
+namespace ntp_snippets {
+
+MockCategoryRanker::MockCategoryRanker() = default;
+
+MockCategoryRanker::~MockCategoryRanker() = default;
+
+}  // namespace ntp_snippets