Chrome extensions can access CPU and GPU statistics via a public API that any extension developer can use. Google Chrome comes bundled with a hidden "Hangouts Services" extension, which has permissions for *.google.com (that extension's ID is the 'nkeimhogjdpnpccoofpliimaahmaaome' referenced in the examples). That extension has a function that will return those stats when called from JavaScript running on a webpage. As a result, any JavaScript running on *.google.com can get the current CPU and GPU utilization.

Hmm. I'm going to go ahead and blame twitter here. I don't see any additional links in the tweet or anything.

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There is a link pointing out the exact place in Chrome's code.