Move FakeAttachmentStore from IO thread to FILE thread.

BUG=

Review URL: https://codereview.chromium.org/292583002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271821 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/sync/profile_sync_components_factory_impl.cc

@@ -577,7 +577,7 @@ ProfileSyncComponentsFactoryImpl::CreateAttachmentService(
 
   scoped_ptr<syncer::AttachmentStore> attachment_store(
       new syncer::FakeAttachmentStore(
-          BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO)));
+          BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE)));
 
   scoped_ptr<syncer::AttachmentService> attachment_service(
       new syncer::AttachmentServiceImpl(