[NTP Snippets] NTPSnippetsService: notify about new suggestions only in changed categories

components/ntp_snippets/content_suggestions_service.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/content_suggestions_service.h"
 
 #include <algorithm>
 #include <iterator>
 #include <set>
 #include <utility>
@@ skipping 184 matching lines @@
   providers_.push_back(std::move(provider));
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // Private methods
 
 void ContentSuggestionsService::OnNewSuggestions(
     ContentSuggestionsProvider* provider,
     Category category,
     std::vector<ContentSuggestion> suggestions) {
+  // Providers shouldn't call this when they're in a non-available state.
+  DCHECK(
+      IsCategoryStatusInitOrAvailable(provider->GetCategoryStatus(category)));
+
   if (TryRegisterProviderForCategory(provider, category)) {
     NotifyCategoryStatusChanged(category);
   } else if (IsCategoryDismissed(category)) {
     // The category has been registered as a dismissed one. We need to
     // check if the dismissal can be cleared now that we received new data.
     if (suggestions.empty())
       return;
 
     RestoreDismissedCategory(category);
     StoreDismissedCategoriesToPrefs();
@@ skipping 209 matching lines @@
 void ContentSuggestionsService::StoreDismissedCategoriesToPrefs() {
   base::ListValue list;
   for (const auto& category_provider_pair : dismissed_providers_by_category_) {
     list.AppendInteger(category_provider_pair.first.id());
   }
 
   pref_service_->Set(prefs::kDismissedCategories, list);
 }
 
 }  // namespace ntp_snippets