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

components/ntp_snippets/category_rankers/constant_category_ranker.h

Index: components/ntp_snippets/category_rankers/constant_category_ranker.h
diff --git a/components/ntp_snippets/category_rankers/constant_category_ranker.h b/components/ntp_snippets/category_rankers/constant_category_ranker.h
new file mode 100644
index 0000000000000000000000000000000000000000..bf940e6fac8c68d979e6ff93d9ee006c68ef8e29
--- /dev/null
+++ b/components/ntp_snippets/category_rankers/constant_category_ranker.h
@@ -0,0 +1,38 @@
+// 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_CONSTANT_SECTION_RANKER_H_
+#define COMPONENTS_NTP_SNIPPETS_SECTION_RANKERS_CONSTANT_SECTION_RANKER_H_
+
+#include <vector>
+
+#include "base/time/time.h"
+#include "components/ntp_snippets/category.h"
+#include "components/ntp_snippets/category_rankers/category_ranker.h"
+
+namespace ntp_snippets {
+
+// TODO(vitaliii): Add unit tests.

[tschumann, 2016/12/15 11:50:26]

i treat this as a DO_NOT_SUBMIT ;-) Not sure if this works in chromium though...

[vitaliii, 2016/12/15 15:30:13]

The idea was to submit this large CL and then immediately proceed with tests.
However, Marc noticed this and in the end I rewrote former CategoryFactory tests
and added new ones.

[tschumann, 2016/12/15 18:23:13]

:-)  I totally got that idea and disagreed ;-). If the CL would have been too
big, then we'd simply split out a CL (say adding the ConstantCategoryRanker +
tests) submit that first and then submit the CL to integrate it.
Never submit new classes without tests -- even with the best intentions, people
rarely get back at "TODO() add tests". That aside, we don't want untested code
to end up in canary and create crashes and bug report noise.

Thanks for adding them !! :-D

[vitaliii, 2016/12/16 08:15:43]

Ack.

Now I see, fair enough.

+class ConstantCategoryRanker : public CategoryRanker {
+ public:
+  ConstantCategoryRanker();
+  virtual ~ConstantCategoryRanker();
+
+  // CategoryRanker implementation.
+  bool Compare(Category left, Category right) const override;
+  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(ConstantCategoryRanker);
+};
+
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_SECTION_RANKERS_CONSTANT_SECTION_RANKER_H_