This was something that was requested in https://github.com/backdrop/backdrop-issues/issues/1087#issuecomment-172...
With this plugin, CKEditor will automatically expand and shrink vertically depending on the amount and size of content entered in its editing area.
The following configuration options are available:
- maximum and minimum editor height after adjustment to content,
- extra space to be added between content and editor bottom bar,
- having auto grow happen on editor startup