[NTP::SectionOrder] Propagate new order through ContentSuggestionsService.

components/ntp_snippets/content_suggestions_service.h

Index: components/ntp_snippets/content_suggestions_service.h
diff --git a/components/ntp_snippets/content_suggestions_service.h b/components/ntp_snippets/content_suggestions_service.h
index 8ad6b60afc2150c8a214d113fbc8a3f95efdc89f..c7dfbe5333c9165fb43dea82133d6a8399d58a57 100644
--- a/components/ntp_snippets/content_suggestions_service.h
+++ b/components/ntp_snippets/content_suggestions_service.h
@@ -100,9 +100,10 @@ class ContentSuggestionsService : public KeyedService,
 
   State state() { return state_; }
 
-  // Gets all categories for which a provider is registered. The categories
-  // may or may not be available, see |GetCategoryStatus()|.
-  const std::vector<Category>& GetCategories() const { return categories_; }
+  // Gets all categories for which a provider is registered. The categories may
+  // or may not be available, see |GetCategoryStatus()|. The order is obtained
+  // from |category_ranker_| immediately.

[tschumann, 2016/12/19 09:06:38]

IMO, this comment is exposing too many implementation details. What's important
is that the order in which the categories are returned is the order in which
they should be displayed.
It doesn't matter how or with which members the service is computing this order.

[vitaliii, 2016/12/19 11:31:39]

Done.

+  const std::vector<Category>& GetCategories();
 
   // Gets the status of a category.
   CategoryStatus GetCategoryStatus(Category category) const;
@@ -285,8 +286,9 @@ class ContentSuggestionsService : public KeyedService,
       dismissed_providers_by_category_;
 
   // All current suggestion categories, in an order determined by the
-  // |category_factory_|. This vector contains exactly the same categories as
-  // |providers_by_category_|.
+  // |category_ranker_|. The order here may be stale, i.e. changes in the ranker

[tschumann, 2016/12/19 09:06:38]

nit: let's phrase this a bit clearer:
The order in categories_ is not specified.

Also, please don't add too many implementation details -- it'll get out of sync
with the implementation (no need to mention SortCategories() or the ranker).
The last sentence is worth keeping though.

[vitaliii, 2016/12/19 11:31:39]

Done.

+  // are not immediately propagated here (use SortCategories() to refresh). This
+  // vector contains exactly the same categories as |providers_by_category_|.
   std::vector<Category> categories_;
 
   // All current suggestions grouped by category. This contains an entry for