UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.75 Safari/537.36

Example URL:
https://www.youtube.com/watch?v=cIyVNoY3_L4

Steps to reproduce the problem:
1. Use a Kaby Lake (Intel's 7th gen) machine, which has a VP9 hardware decoder https://en.wikipedia.org/wiki/Kaby_Lake (like the updated with Kaby Lake HP Spectre x360).
2. Play a 4K video on YouTube, such as https://www.youtube.com/watch?v=cIyVNoY3_L4. 
3. Observe in stats for nerds (right click on the YouTube player) that it's using VP9, and in 4K stutters terribly, drops frames, and uses up 60-100% CPU.
4. The same problem does not appear in Edge or Firefox, also using VP9 (confirmed with stats for nerds), or after enabling this Chrome extension that forces H264 https://chrome.google.com/webstore/detail/h264ify/aleakchihdccplidncghkekgioiakgal?hl=en-US. In these cases, no drops in frames occur, and CPU usage hovers around 5-15%.
5. Cry silently in a corner seeing as how Chrome is seemingly unable to utilize hardware decoding of VP9 videos on Kaby Lake. 

What is the expected behavior?

What went wrong?
Chrome dropped frames, used lots of CPU and battery (fans spinning max speed). Other competitors did not.

Did this work before? No 

Is it a problem with Flash or HTML5? HTML5

Does this work in other browsers? Yes

Chrome version: 55.0.2883.75  Channel: stable
OS Version: 10.0
Flash Version: Shockwave Flash 23.0 r0

See https://plus.google.com/+ArtemRussakovskii/posts/4sF6o9tbR9s for a discussion.

Other discussions/bugs around the web seem to revolve around VP9 requiring software decoding on older CPUs, but in the case of Kaby Lake, we should be looking at hardware decoding, which is why this is a separate bug.