You used to be able to go to chrome://flags/ and then enable FPS counter, but I just looked and it appears that Google moved this feature so it's a little less convenient. Now you have to access the FPS counter through DevTools:
1. Use CTRL+SHIFT+I to open DevTools.
2. Look for "Console" heading, which should be toward the bottom of the page.
3. Click on the menu bar (three verticle dots) beside "Console," and select "Rendering" from the drop-down list.
4. You should see "Show FPS meter" with a check box beside it. Check the box to enable the FPS meter.