message: don't override display name even if it is empty, otherewise, it could use src->name as dst->display_name.
diff: @@ -239,9 +239,8 @@ void MergePlanes(const XPlane& src_plane, XPlane* dst_plane) {
  EnvTime::kNanosToPicos;
  }
  dst_line.SetNameIfEmpty(line.Name());
  - if (!line.DisplayName().empty()) {
  - dst_line.SetDisplayNameIfEmpty(line.DisplayName());
  - }
  + // Don't override dst_line's display name because if both lines have name,
  + // but no display name, line's name will became display name of dst_line.
  }
  line.ForEachEvent([&](const tensorflow::profiler::XEventVisitor& event) {
  