Add a minimal AttachmentUploaderImpl.

sync/internal_api/attachments/fake_attachment_uploader.cc

 // Copyright 2014 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 "sync/internal_api/public/attachments/fake_attachment_uploader.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "sync/api/attachments/attachment.h"
+#include "sync/protocol/sync.pb.h"
 
 namespace syncer {
 
 FakeAttachmentUploader::FakeAttachmentUploader() {
   DCHECK(CalledOnValidThread());
 }
 
 FakeAttachmentUploader::~FakeAttachmentUploader() {
   DCHECK(CalledOnValidThread());
 }
 
 void FakeAttachmentUploader::UploadAttachment(const Attachment& attachment,
                                               const UploadCallback& callback) {
   DCHECK(CalledOnValidThread());
+  DCHECK(!attachment.GetId().GetProto().unique_id().empty());
+
   UploadResult result = UPLOAD_SUCCESS;
   AttachmentId updated_id = attachment.GetId();
   // TODO(maniscalco): Update the attachment id with server address information
   // before passing it to the callback.
   base::MessageLoop::current()->PostTask(
       FROM_HERE, base::Bind(callback, result, updated_id));
 }
 
 }  // namespace syncer