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

components/ntp_snippets/section_rankers/default_constant_section_ranker.h

+// 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_SECTION_RANKERS_DEFAULT_CONSTANT_SECTION_RANKER_H_
+#define COMPONENTS_NTP_SNIPPETS_SECTION_RANKERS_DEFAULT_CONSTANT_SECTION_RANKER_H_
+
+#include <vector>
+
+#include "base/time/time.h"
+#include "components/ntp_snippets/category.h"
+#include "components/ntp_snippets/section_rankers/section_ranker.h"
+
+namespace ntp_snippets {
+
+// TODO(vitaliii): Add unit tests.

[Marc Treib, 2016/12/13 12:22:42]

Yes please. At the very least, port the CategoryFactoryTests over.

[vitaliii, 2016/12/14 08:59:38]

But not in this CL.

[Marc Treib, 2016/12/14 10:24:31]

No need to write additional tests in this CL, but you removed a number of
CategoryFactoryTests. Those should be re-added as CategoryRankerTests in this
CL.

[vitaliii, 2016/12/15 15:30:12]

Done.

+class DefaultConstantSectionRanker : public SectionRanker {

[Marc Treib, 2016/12/13 12:22:42]

Remove the "Default" - that's not part of the class definition, and it's bound
to change (hopefully!)

[vitaliii, 2016/12/14 08:59:38]

Done.

+ public:
+  DefaultConstantSectionRanker();
+  virtual ~DefaultConstantSectionRanker();
+
+  bool Compare(Category left, Category right) const override;

[Marc Treib, 2016/12/13 12:22:42]

nitty nit: Add a "CategoryRanker implementation." comment, and remove the empty
lines between the methods?

[vitaliii, 2016/12/14 08:59:38]

Done.

+
+  void ClearHistory(base::Time begin, base::Time end) override;
+
+  void AppendCategoryIfNecessary(Category category) override;
+
+  void OnSuggestionOpened(Category category) override;
+
+ private:
+  void AppendKnownCategory(KnownCategories known_category);
+
+  std::vector<Category> ordered_categories_;
+
+  DISALLOW_COPY_AND_ASSIGN(DefaultConstantSectionRanker);
+};
+
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_SECTION_RANKERS_DEFAULT_CONSTANT_SECTION_RANKER_H_