Maybe a lot of people know of this already, but I definitely only found out about this this past week, so I thought I'd share.
There's a really easy way to emulate devices / browser sizes, so you don't have to manually resize the browser, or download some extension to do spoofing, and is a viable alternative to iOS simulator.
Open up Chrome's inspector tool, click the gear icon, and turn on 'Show 'Emulation' view in the console drawer'.
Then, open up the console, and switch to the emulation tab, where you can emulate devices / user agents, set resolutions, even set the pixel ratio.
Hope this helps some people.