You can click the settings icon on top right corner ...
| More Tools | Developer Tools | Network | Disable cache (while DevTools is open)
For windows, this is F12 or CTRL + SHIFT + I while on mac CMD + SHIFT + I opens up DevTools.
New path for Chrome Update Sept 2018:
Click settings icon on the top right corner ...
| Settings | Preferences | Developer Tools | Network | Disable cache (while DevTools is open)