message: Add move constructor/assignment
diff: @@ -73,6 +73,9 @@ class LayoutItem {
  LayoutItem(const LayoutItem&) = default;
  LayoutItem& operator=(const LayoutItem&) = default;
  + LayoutItem(LayoutItem&&) = default;
  + LayoutItem& operator=(LayoutItem&&) = default;
  +
  LayoutType Type() const { return type_; }
  // Returns "hard" indent, which is never removed when the layout is joined
  