Chrome cannot resize horizontally below 400px (OS X) or 218px (Windows) but I have a really simple solution to the problem:
- Dock the web inspector to the right instead of to the bottom
- Resize the inspector panel – you can now make the browser area really small (down to 0px)
Update: Chrome now allows you to arrange the inspector windows vertically when docked to the right! This really improves the layout.
The HTML and CSS panels fit really well and you even open a small console panel too.
This has allowed me to completely move from Firefox/Firebug to Chrome.
If you want to go a step further look at the web inspector settings (cog icon, bottom-right), and goto the user agent tab. You can set the screen resolution to whatever you like here and even quickly toggle between portrait and landscape.
UPDATE: Here is another really cool tool I’ve come across. http://lab.maltewassermann.com/viewport-resizer/