Update sync API to support attachments.

sync/protocol/proto_value_conversions.h

Index: sync/protocol/proto_value_conversions.h
diff --git a/sync/protocol/proto_value_conversions.h b/sync/protocol/proto_value_conversions.h
index b09e50a8361049f9ad97a2d759b50ec38a2793cf..bf936eec2e4a39b93b5528f7465d3f0a0e1f4603 100644
--- a/sync/protocol/proto_value_conversions.h
+++ b/sync/protocol/proto_value_conversions.h
@@ -20,6 +20,7 @@ class AppNotificationSettings;
 class AppSettingSpecifics;
 class AppSpecifics;
 class ArticleSpecifics;
+class AttachmentIdProto;
 class AutofillProfileSpecifics;
 class AutofillSpecifics;
 class BookmarkSpecifics;
@@ -296,6 +297,9 @@ base::DictionaryValue* SyncCycleCompletedEventInfoToValue(
 base::DictionaryValue* ClientConfigParamsToValue(
     const sync_pb::ClientConfigParams& proto);
 
+SYNC_EXPORT_PRIVATE base::DictionaryValue* AttachmentIdProtoToValue(
+    const sync_pb::AttachmentIdProto& proto);
+
 }  // namespace syncer
 
 #endif  // SYNC_PROTOCOL_PROTO_VALUE_CONVERSIONS_H_