Update 05/16/2016: Chrome seems to have added the feature back in! I still like the plugin I found, and I’m going to keep using it.
Chrome seems to have removed the ability to see the browser width as you resize your browser with the dev tools open. In previous versions, you could see the viewport dimensions in the upper left of the browser window as seen below.
With this useful tool gone, I took a look around and found a great replacement in the Window Resizer plugin. This plugin shows the viewport size even when Chrome’s dev tools are closed, and it also has options to automatically resize the window to several common screen sizes.
I can’t possibly imagine why such a useful feature was removed, though it looks like it may be coming back in a future release. I’ll probably still keep the Window Resizer plugin installed, as I really like seeing the dimensions without having to open the dev tools.