The new emulation feature in Chrome is great - within the browser you have the ability to emulate the screen size and network speed of different devices. When you don't want to use it however, it's quite intrusive, and the off button is very suttle!
Taken directly from the Chrome documentation, there's a small device icon that looks like a smart phone you can use to toggle between emulation mode, which will remove all the additional rulers and options:
For shortcut enthusiasts you can also use the following on PC or Mac to toggle the emulation mode in Chrome:
Ctrl+Shift+M (or Cmd+Shift+M on Mac).