Call FetchImageCallback asynchronously when no thumbnail exists

components/ntp_snippets/offline_pages/offline_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/offline_pages/offline_page_suggestions_provider.h"
 
 #include "base/bind.h"
+#include "base/location.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "ui/gfx/image/image.h"
 
 using offline_pages::MultipleOfflinePageItemResult;
 using offline_pages::OfflinePageModel;
 using offline_pages::OfflinePageItem;
 
 namespace ntp_snippets {
 
 namespace {
 
 const int kMaxSuggestionsCount = 5;
@@ skipping 31 matching lines @@
 
 void OfflinePageSuggestionsProvider::DismissSuggestion(
     const std::string& suggestion_id) {
   // TODO(pke): Implement some "dont show on NTP anymore" behaviour,
   // then also implement ClearDismissedSuggestionsForDebugging.
 }
 
 void OfflinePageSuggestionsProvider::FetchSuggestionImage(
     const std::string& suggestion_id,
     const ImageFetchedCallback& callback) {
-  // TODO(pke): Implement.
+  // TODO(pke): Fetch proper thumbnail from OfflinePageModel once it's available
+  // there.
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, base::Bind(callback, suggestion_id, gfx::Image()));
 }
 
 void OfflinePageSuggestionsProvider::ClearCachedSuggestionsForDebugging() {
   // Ignored.
 }
 
 void OfflinePageSuggestionsProvider::ClearDismissedSuggestionsForDebugging() {
   // TODO(pke): Implement when dismissed suggestions are supported.
 }
 
@@ skipping 52 matching lines @@
 void OfflinePageSuggestionsProvider::NotifyStatusChanged(
     CategoryStatus new_status) {
   if (category_status_ == new_status)
     return;
   category_status_ = new_status;
 
   observer()->OnCategoryStatusChanged(this, provided_category_, new_status);
 }
 
 }  // namespace ntp_snippets