Call FetchImageCallback asynchronously when no thumbnail exists

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 "base/bind.h"
+#include "base/location.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "ui/gfx/image/image.h"
 
 namespace ntp_snippets {
 
 bool ContentSuggestionsService::CompareCategoriesByID::operator()(
     const Category& left,
     const Category& right) const {
   return left.id() < right.id();
 }
 
@@ skipping 32 matching lines @@
   if (iterator == suggestions_by_category_.end())
     return no_suggestions_;
   return iterator->second;
 }
 
 void ContentSuggestionsService::FetchSuggestionImage(
     const std::string& suggestion_id,
     const ImageFetchedCallback& callback) {
   if (!id_category_map_.count(suggestion_id)) {
     LOG(WARNING) << "Requested image for unknown suggestion " << suggestion_id;
-    callback.Run(suggestion_id, gfx::Image());
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(callback, suggestion_id, gfx::Image()));
     return;
   }
   Category category = id_category_map_.at(suggestion_id);
   if (!providers_by_category_.count(category)) {
     LOG(WARNING) << "Requested image for suggestion " << suggestion_id
                  << " for unavailable category " << category;
-    callback.Run(suggestion_id, gfx::Image());
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(callback, suggestion_id, gfx::Image()));
     return;
   }
   providers_by_category_[category]->FetchSuggestionImage(suggestion_id,
                                                          callback);
 }
 
 void ContentSuggestionsService::ClearCachedSuggestionsForDebugging() {
   suggestions_by_category_.clear();
   id_category_map_.clear();
   for (auto& category_provider_pair : providers_by_category_) {
@@ skipping 130 matching lines @@
   return true;
 }
 
 void ContentSuggestionsService::NotifyCategoryStatusChanged(Category category) {
   FOR_EACH_OBSERVER(
       Observer, observers_,
       OnCategoryStatusChanged(category, GetCategoryStatus(category)));
 }
 
 }  // namespace ntp_snippets