[NTP Snippets] Always show the bookmarks section, but at the end if it's empty

components/ntp_snippets/content_suggestions_service.cc

Index: components/ntp_snippets/content_suggestions_service.cc
diff --git a/components/ntp_snippets/content_suggestions_service.cc b/components/ntp_snippets/content_suggestions_service.cc
index 1da49f5cfd53dda8781c150fa113ec6be6c49cc9..5a983f423832d440025859ada0dec20eeb99ca3f 100644
--- a/components/ntp_snippets/content_suggestions_service.cc
+++ b/components/ntp_snippets/content_suggestions_service.cc
@@ -179,6 +179,11 @@ void ContentSuggestionsService::OnNewSuggestions(
 
   suggestions_by_category_[category] = std::move(new_suggestions);
 
+  // The positioning of the bookmarks category depends on whether it's empty.
+  // TODO(treib): Remove this temporary hack, crbug.com/640568.
+  if (category.IsKnownCategory(KnownCategories::BOOKMARKS))
+    SortCategories();
+
   FOR_EACH_OBSERVER(Observer, observers_, OnNewSuggestions(category));
 }
 
@@ -227,10 +232,7 @@ bool ContentSuggestionsService::RegisterCategoryIfRequired(
 
   providers_by_category_[category] = provider;
   categories_.push_back(category);
-  std::sort(categories_.begin(), categories_.end(),
-            [this](const Category& left, const Category& right) {
-              return category_factory_.CompareCategories(left, right);
-            });
+  SortCategories();
   if (IsCategoryStatusAvailable(provider->GetCategoryStatus(category))) {
     suggestions_by_category_.insert(
         std::make_pair(category, std::vector<ContentSuggestion>()));
@@ -252,6 +254,12 @@ bool ContentSuggestionsService::RemoveSuggestionByID(
   if (position == suggestions->end())
     return false;
   suggestions->erase(position);
+
+  // The positioning of the bookmarks category depends on whether it's empty.
+  // TODO(treib): Remove this temporary hack, crbug.com/640568.
+  if (category.IsKnownCategory(KnownCategories::BOOKMARKS))
+    SortCategories();
+
   return true;
 }
 
@@ -261,4 +269,24 @@ void ContentSuggestionsService::NotifyCategoryStatusChanged(Category category) {
       OnCategoryStatusChanged(category, GetCategoryStatus(category)));
 }
 
+void ContentSuggestionsService::SortCategories() {
+  auto it = suggestions_by_category_.find(
+      category_factory_.FromKnownCategory(KnownCategories::BOOKMARKS));
+  bool bookmarks_empty =
+      (it == suggestions_by_category_.end() || it->second.empty());
+  std::sort(
+      categories_.begin(), categories_.end(),
+      [this, bookmarks_empty](const Category& left, const Category& right) {
+        // If the bookmarks section is empty, put it at the end.
+        // TODO(treib): This is a temporary hack, see crbug.com/640568.
+        if (bookmarks_empty) {
+          if (left.IsKnownCategory(KnownCategories::BOOKMARKS))
+            return false;
+          if (right.IsKnownCategory(KnownCategories::BOOKMARKS))
+            return true;
+        }
+        return category_factory_.CompareCategories(left, right);
+      });
+}
+
 }  // namespace ntp_snippets