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

components/ntp_snippets/category_rankers/mock_category_ranker.h

Index: components/ntp_snippets/category_rankers/mock_category_ranker.h
diff --git a/components/ntp_snippets/category_rankers/mock_category_ranker.h b/components/ntp_snippets/category_rankers/mock_category_ranker.h
new file mode 100644
index 0000000000000000000000000000000000000000..2828167956771e76daa862166914d1ad776dfdd1
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+++ b/components/ntp_snippets/category_rankers/mock_category_ranker.h
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+// 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.
+
+#ifndef COMPONENTS_NTP_SNIPPETS_CATEGORY_RANKERS_MOCK_CATEGORY_RANKER_H_
+#define COMPONENTS_NTP_SNIPPETS_CATEGORY_RANKERS_MOCK_CATEGORY_RANKER_H_
+
+#include "base/time/time.h"
+#include "components/ntp_snippets/category.h"
+#include "components/ntp_snippets/category_rankers/category_ranker.h"
+#include "testing/gmock/include/gmock/gmock.h"
+
+namespace ntp_snippets {
+
+class MockCategoryRanker : public CategoryRanker {
+ public:
+  MockCategoryRanker();
+  ~MockCategoryRanker() override;
+
+  MOCK_CONST_METHOD2(Compare, bool(Category left, Category right));
+  MOCK_METHOD2(ClearHistory, void(base::Time begin, base::Time end));
+  MOCK_METHOD1(AppendCategoryIfNecessary, void(Category category));
+  MOCK_METHOD1(OnSuggestionOpened, void(Category category));
+};
+
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_CATEGORY_RANKERS_MOCK_CATEGORY_RANKER_H_