Update Commit and GetUpdatesResponse messages to include attachment ids.

sync/internal_api/syncapi_internal.cc

Index: sync/internal_api/syncapi_internal.cc
diff --git a/sync/internal_api/syncapi_internal.cc b/sync/internal_api/syncapi_internal.cc
index d297fcba6cc3a0f6a2f3e2f6c81c99280bb63b8c..91a6d79fd1b47417ec7a788df4a23258b3f57868 100644
--- a/sync/internal_api/syncapi_internal.cc
+++ b/sync/internal_api/syncapi_internal.cc
@@ -5,6 +5,7 @@
 #include "sync/internal_api/syncapi_internal.h"
 
 #include "base/memory/scoped_ptr.h"
+#include "sync/protocol/attachments.pb.h"
 #include "sync/protocol/password_specifics.pb.h"
 #include "sync/protocol/sync.pb.h"
 #include "sync/util/cryptographer.h"
@@ -104,4 +105,12 @@ bool AreSpecificsEqual(const Cryptographer* cryptographer,
   return false;
 }
 
+bool AreAttachmentMetadataEqual(const sync_pb::AttachmentMetadata& left,
+                                const sync_pb::AttachmentMetadata& right) {
+  if (left.SerializeAsString() == right.SerializeAsString()) {
+    return true;
+  }
+  return false;
+}
+
 }  // namespace syncer