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..10365afddd35f9e14661c9cbb330ef328a128332 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,
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::DB)));

[stuartmorgan, 2015/06/10 18:18:17]

This needs to use WebThread, not BrowserThread. I'm not actually sure how this
compiled, since content/ headers shouldn't be bleeding into this code, ideally.

But there's also an active effort underway to eliminate MessageLoopProxy in
general, and as part of that WebThread had the MLP methods removed. Why isn't
this using SingleThreadedTaskRunner?

[Sami, 2015/06/10 18:40:15]

BrowserThread::GetMessageLoopProxyForThread returns a SingleThreadTaskRunner --
we just haven't renamed it yet :\

But yeah, looks like this should be calling WebThread::GetTaskRunnerForThread().

   return new SuggestionsService(
       browser_state->GetRequestContext(), suggestions_store.Pass(),
       thumbnail_manager.Pass(), blacklist_store.Pass());