Update Commit and GetUpdatesResponse messages to include attachment ids.

sync/internal_api/syncapi_internal.h

 // Copyright 2012 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.
 
 #ifndef SYNC_INTERNAL_API_SYNCAPI_INTERNAL_H_
 #define SYNC_INTERNAL_API_SYNCAPI_INTERNAL_H_
 
 // The functions defined are shared among some of the classes that implement
 // the internal sync API.  They are not to be used by clients of the API.
 
 #include <string>
 
 #include "sync/base/sync_export.h"
 
 namespace sync_pb {
+class AttachmentMetadata;
 class EntitySpecifics;
 class PasswordSpecificsData;
 }
 
 namespace syncer {
 
 class Cryptographer;
 
 sync_pb::PasswordSpecificsData* DecryptPasswordSpecifics(
     const sync_pb::EntitySpecifics& specifics,
     Cryptographer* crypto);
 
 SYNC_EXPORT void SyncAPINameToServerName(const std::string& syncer_name,
                                          std::string* out);
 SYNC_EXPORT void ServerNameToSyncAPIName(const std::string& server_name,
                                          std::string* out);
 
 bool IsNameServerIllegalAfterTrimming(const std::string& name);
 
 bool AreSpecificsEqual(const Cryptographer* cryptographer,
                        const sync_pb::EntitySpecifics& left,
                        const sync_pb::EntitySpecifics& right);
+
+// Return true iff |left| and |right| are equal.
+bool AreAttachmentMetadataEqual(const sync_pb::AttachmentMetadata& left,
+                                const sync_pb::AttachmentMetadata& right);
+
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_SYNCAPI_INTERNAL_H_