Remove use of deprecated MessageLoop methods in sync.

sync/internal_api/attachments/fake_attachment_downloader.cc

Index: sync/internal_api/attachments/fake_attachment_downloader.cc
diff --git a/sync/internal_api/attachments/fake_attachment_downloader.cc b/sync/internal_api/attachments/fake_attachment_downloader.cc
index cf3f6f0a3ad8b176c22f60a2037f2feab509399a..d55e07661cf179a9697dfb846c049c70ec2d822c 100644
--- a/sync/internal_api/attachments/fake_attachment_downloader.cc
+++ b/sync/internal_api/attachments/fake_attachment_downloader.cc
@@ -5,7 +5,9 @@
 #include "sync/internal_api/public/attachments/fake_attachment_downloader.h"
 
 #include "base/bind.h"
-#include "base/message_loop/message_loop.h"
+#include "base/location.h"
+#include "base/single_thread_task_runner.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "sync/internal_api/public/attachments/attachment_util.h"
 
 namespace syncer {
@@ -27,7 +29,7 @@ void FakeAttachmentDownloader::DownloadAttachment(
   std::unique_ptr<Attachment> attachment;
   attachment.reset(
       new Attachment(Attachment::CreateFromParts(attachment_id, data)));
-  base::MessageLoop::current()->PostTask(
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE,
       base::Bind(callback, DOWNLOAD_SUCCESS, base::Passed(&attachment)));
 }