Decode ImageManager cached images on demand.

ios/chrome/browser/suggestions/suggestions_service_factory.mm

Index: ios/chrome/browser/suggestions/suggestions_service_factory.mm
diff --git a/ios/chrome/browser/suggestions/suggestions_service_factory.mm b/ios/chrome/browser/suggestions/suggestions_service_factory.mm
index bc08640022a67a5c7ee7a91f0cbd9cdcf56f6715..f185973b7d990013374cc97ab59e1620c5d41535 100644
--- a/ios/chrome/browser/suggestions/suggestions_service_factory.mm
+++ b/ios/chrome/browser/suggestions/suggestions_service_factory.mm
@@ -68,8 +68,9 @@ KeyedService* SuggestionsServiceFactory::BuildServiceInstanceFor(
       new leveldb_proto::ProtoDatabaseImpl<ImageData>(background_task_runner));
   scoped_ptr<ImageFetcher> image_fetcher(new ImageFetcherImpl(
       browser_state->GetRequestContext(), sequenced_worker_pool));
-  scoped_ptr<ImageManager> thumbnail_manager(
-      new ImageManager(image_fetcher.Pass(), db.Pass(), database_dir));
+  scoped_ptr<ImageManager> thumbnail_manager(new ImageManager(
+      image_fetcher.Pass(), db.Pass(), database_dir,
+      web::WebThread::GetTaskRunnerForThread(web::WebThread::DB)));
   return new SuggestionsService(
       browser_state->GetRequestContext(), suggestions_store.Pass(),
       thumbnail_manager.Pass(), blacklist_store.Pass());