According to Gizmodo, Chrome 57 does this through what they call the “throttling policy,” which has something to do with limiting the activity of background tabs.
It basically works by first identifying tabs that are working in the background. These tabs will then be limited to just one percent of the CPU core’s power.
The method is found to have saved up to 25 percent of a device’s power following rigorous tests.
But the throttling policy doesn’t always limit all the tabs that you leave running in the background.
For example, background tabs that are streaming music will definitely be left alone for obvious reasons. The same goes for video chat and messenger apps that need to remain active to function properly.
You can check out the other features of Chrome 57 in the video below.