Fix handling of undeletion within the syncer.

chrome/browser/sync/engine/syncproto.h

Index: chrome/browser/sync/engine/syncproto.h
diff --git a/chrome/browser/sync/engine/syncproto.h b/chrome/browser/sync/engine/syncproto.h
index 3b9acb0ba5b90269a0981ea8befab09c30aa5405..b8f0a75a56c070233fb068f0a6a3d619aff849cb 100644
--- a/chrome/browser/sync/engine/syncproto.h
+++ b/chrome/browser/sync/engine/syncproto.h
@@ -19,6 +19,9 @@ namespace browser_sync {
 template<class Base>
 class IdWrapper : public Base {
  public:
+  IdWrapper() {}
+  explicit IdWrapper(const Base& other) : Base(other) {
+  }
   syncable::Id id() const {
     return syncable::Id::CreateFromServerId(Base::id_string());
   }
@@ -31,6 +34,11 @@ class IdWrapper : public Base {
 // them directly.
 class SyncEntity : public IdWrapper<sync_pb::SyncEntity> {
  public:
+  SyncEntity() {}
+  explicit SyncEntity(const sync_pb::SyncEntity& other)
+      : IdWrapper<sync_pb::SyncEntity>(other) {
+  }
+
   void set_parent_id(const syncable::Id& id) {
     set_parent_id_string(id.GetServerId());
   }