Make GetDismissedSuggestionsForDebugging asynchronous

components/ntp_snippets/physical_web_pages/physical_web_page_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/physical_web_pages/physical_web_page_suggestions_provider.h"
 
 #include "base/bind.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 71 matching lines @@
 void PhysicalWebPageSuggestionsProvider::FetchSuggestionImage(
     const std::string& suggestion_id, const ImageFetchedCallback& callback) {
   // TODO(vitaliii): Implement.
 }
 
 void PhysicalWebPageSuggestionsProvider::ClearCachedSuggestionsForDebugging(
     Category category) {
   // Ignored
 }
 
-std::vector<ContentSuggestion>
-PhysicalWebPageSuggestionsProvider::GetDismissedSuggestionsForDebugging(
-    Category category) {
+void PhysicalWebPageSuggestionsProvider::GetDismissedSuggestionsForDebugging(
+    Category category,
+    const DismissedSuggestionsCallback& callback) {
   // Not implemented.
-  return std::vector<ContentSuggestion>();
+  callback.Run(std::vector<ContentSuggestion>());
 }
 
 void PhysicalWebPageSuggestionsProvider::ClearDismissedSuggestionsForDebugging(
     Category category) {
   // TODO(vitaliii): Implement when dismissed suggestions are supported.
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // Private methods
 
 // Updates the |category_status_| and notifies the |observer_|, if necessary.
 void PhysicalWebPageSuggestionsProvider::NotifyStatusChanged(
     CategoryStatus new_status) {
   if (category_status_ == new_status) return;
   category_status_ = new_status;
   observer()->OnCategoryStatusChanged(this, provided_category_, new_status);
 }
 
 }  // namespace ntp_snippets