Yes, it is a Chrome limitation. The next version will provide the option to open the window as a pop-up, which could be resized to widths lower than 400, but, until then, you can drag the following link to your bookmarks toolbar and click on it to open any tab as a pop-up. Then, you can use the right-click menu to access the resize options.
Bookmark this -> Pop-up
Thank you. The pop up bookmark works great. I look forward to this being added to the Window Resizer extension in the future.
Customer support service by UserEcho