Make GetDismissedSuggestionsForDebugging asynchronous

components/ntp_snippets/physical_web_pages/physical_web_page_suggestions_provider.h

 // 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_PHYSICAL_WEB_PAGES_PHYSICAL_WEB_PAGE_SUGGESTIONS_PROVIDER_H_
 #define COMPONENTS_NTP_SNIPPETS_PHYSICAL_WEB_PAGES_PHYSICAL_WEB_PAGE_SUGGESTIONS_PROVIDER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 32 matching lines @@
   void OnDisplayableUrlsChanged(const std::vector<UrlInfo>& urls);
 
   // ContentSuggestionsProvider implementation.
   std::vector<Category> GetProvidedCategories() override;
   CategoryStatus GetCategoryStatus(Category category) override;
   CategoryInfo GetCategoryInfo(Category category) override;
   void DismissSuggestion(const std::string& suggestion_id) override;
   void FetchSuggestionImage(const std::string& suggestion_id,
                             const ImageFetchedCallback& callback) override;
   void ClearCachedSuggestionsForDebugging(Category category) override;
-  std::vector<ContentSuggestion> GetDismissedSuggestionsForDebugging(
-      Category category) override;
+  void GetDismissedSuggestionsForDebugging(
+      Category category,
+      const DismissedSuggestionsCallback& callback) override;
   void ClearDismissedSuggestionsForDebugging(Category category) override;
 
  private:
   void NotifyStatusChanged(CategoryStatus new_status);
 
   CategoryStatus category_status_;
   const Category provided_category_;
 
   DISALLOW_COPY_AND_ASSIGN(PhysicalWebPageSuggestionsProvider);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_PHYSICAL_WEB_PAGES_PHYSICAL_WEB_PAGE_SUGGESTIONS_PROVIDER_H_