Add AttachmentUploader interface and fake implementation.

sync/api/attachments/attachment_uploader.cc

Index: sync/api/attachments/attachment_uploader.cc
diff --git a/sync/engine/commit_contribution.cc b/sync/api/attachments/attachment_uploader.cc
similarity index 59%
copy from sync/engine/commit_contribution.cc
copy to sync/api/attachments/attachment_uploader.cc
index cef02b57b9021598370cc9e7554ab15042a9489a..db081b1c96a89c70124e6b305ab6806fcacb88a8 100644
--- a/sync/engine/commit_contribution.cc
+++ b/sync/api/attachments/attachment_uploader.cc
@@ -2,12 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "sync/engine/commit_contribution.h"
+#include "sync/api/attachments/attachment_uploader.h"
 
 namespace syncer {
 
-CommitContribution::CommitContribution() {}
-
-CommitContribution::~CommitContribution() {}
+AttachmentUploader::AttachmentUploader() {
+}
+AttachmentUploader::~AttachmentUploader() {
+}
 
 }  // namespace syncer