Steps to reproduce: - In a snippet in grid mode, resize a column. - Drag and drop this column in a non-grid dropzone. - Undo. => The column is back in the grid but is still a normal column. The same happens when doing these steps with a normal column to a grid. This happens because the class changes are not observed in these cases. When fixing the drag and drop history in [1], only the style changes were observed because the class changes are automatically recorded. But it is not the case after a resize. This commit fixes that by also observing the class changes. [1]: https://github.com/odoo/odoo/commit/1dfb127f70832aa9e9022ac337af343b7dc17729 task-3151207 closes odoo/odoo#117854 X-original-commit: 48b3683c4753f1e385ea1692db9c1a15d32cae30 Signed-off-by: Arthur Detroux (ard) <ard@odoo.com>