Call FetchImageCallback asynchronously when no thumbnail exists

components/ntp_snippets/bookmarks/bookmark_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/bookmarks/bookmark_suggestions_provider.h"
 
 #include <utility>
 #include <vector>
 
+#include "base/bind.h"
+#include "base/location.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "components/bookmarks/browser/bookmark_model.h"
 #include "components/ntp_snippets/bookmarks/bookmark_last_visit_utils.h"
 #include "components/ntp_snippets/category_factory.h"
 #include "components/ntp_snippets/content_suggestion.h"
+#include "ui/gfx/image/image.h"
 
 using bookmarks::BookmarkModel;
 using bookmarks::BookmarkNode;
 
 namespace {
 
 const int kMaxBookmarks = 10;
 const int kMaxBookmarkAgeInDays = 42;
 
 base::Time GetThresholdTime() {
@@ skipping 37 matching lines @@
 
 void BookmarkSuggestionsProvider::DismissSuggestion(
     const std::string& suggestion_id) {
   // TODO(jkrcal): Implement blacklisting bookmarks until they are next visited.
   // Then also implement ClearDismissedSuggestionsForDebugging.
 }
 
 void BookmarkSuggestionsProvider::FetchSuggestionImage(
     const std::string& suggestion_id,
     const ImageFetchedCallback& callback) {
-  callback.Run(suggestion_id, gfx::Image());
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, base::Bind(callback, suggestion_id, gfx::Image()));
 }
 
 void BookmarkSuggestionsProvider::ClearCachedSuggestionsForDebugging() {
   // Ignored.
 }
 
 void BookmarkSuggestionsProvider::ClearDismissedSuggestionsForDebugging() {
   // TODO(jkrcal): Implement when discarded suggestions are supported.
 }
 
@@ skipping 66 matching lines @@
 
 void BookmarkSuggestionsProvider::NotifyStatusChanged(
     CategoryStatus new_status) {
   if (category_status_ == new_status)
     return;
   category_status_ = new_status;
   observer()->OnCategoryStatusChanged(this, provided_category_, new_status);
 }
 
 }  // namespace ntp_snippets