This is basically the respective issue for what is being worked on for D8 core here: https://www.drupal.org/project/drupal/issues/2061377

This is part of #1087 and #378, and related to #2841

2061377-test-273

Original issue summary

It would be great to be able to use image styles within CKEditor so that users could get consistent image sizes/styles within their content.

This is a follow-up from #2010 and #2630 where @Dinornis commented:

Maybe the image sizing can be replaced with the option of selecting an Image style predefined in /admin/config/media/image-styles?

GitHub Link: 
https://github.com/backdrop/backdrop-issues/issues/2658
GitHub Issue #: 
2658