[NTP Snippets] Pass "no suggestions" message from the backend to the UI

components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc

 // 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.
 
 #include "components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 55 matching lines @@
 
 CategoryStatus RecentTabSuggestionsProvider::GetCategoryStatus(
     Category category) {
   if (category == provided_category_)
     return category_status_;
   NOTREACHED() << "Unknown category " << category.id();
   return CategoryStatus::NOT_PROVIDED;
 }
 
 CategoryInfo RecentTabSuggestionsProvider::GetCategoryInfo(Category category) {
-  if (category == provided_category_) {
-    return CategoryInfo(l10n_util::GetStringUTF16(
-                            IDS_NTP_RECENT_TAB_SUGGESTIONS_SECTION_HEADER),
-                        ContentSuggestionsCardLayout::MINIMAL_CARD,
-                        /*has_more_button=*/false,
-                        /*show_if_empty=*/false);
-  }
-  NOTREACHED() << "Unknown category " << category.id();
-  return CategoryInfo(base::string16(),
-                      ContentSuggestionsCardLayout::MINIMAL_CARD,
-                      /*has_more_button=*/false,
-                      /*show_if_empty=*/false);
+  DCHECK_EQ(provided_category_, category);
+  return CategoryInfo(
+      l10n_util::GetStringUTF16(IDS_NTP_RECENT_TAB_SUGGESTIONS_SECTION_HEADER),
+      ContentSuggestionsCardLayout::MINIMAL_CARD,
+      /*has_more_button=*/false,
+      /*show_if_empty=*/false,
+      l10n_util::GetStringUTF16(IDS_NTP_SUGGESTIONS_SECTION_EMPTY));
+  // TODO(vitaliii): Replace IDS_NTP_SUGGESTIONS_SECTION_EMPTY with a
+  // category-specific string.
 }
 
 void RecentTabSuggestionsProvider::DismissSuggestion(
     const ContentSuggestion::ID& suggestion_id) {
   DCHECK_EQ(provided_category_, suggestion_id.category());
   std::set<std::string> dismissed_ids = ReadDismissedIDsFromPrefs();
   dismissed_ids.insert(suggestion_id.id_within_category());
   StoreDismissedIDsToPrefs(dismissed_ids);
 }
 
@@ skipping 167 matching lines @@
 }
 
 void RecentTabSuggestionsProvider::StoreDismissedIDsToPrefs(
     const std::set<std::string>& dismissed_ids) {
   prefs::StoreDismissedIDsToPrefs(pref_service_,
                                   prefs::kDismissedRecentOfflineTabSuggestions,
                                   dismissed_ids);
 }
 
 }  // namespace ntp_snippets