1. Switch youtube.com to the new experience on youtube.com/testtube
2. Open a video, e.g. https://www.youtube.com/watch?v=-rSDUsMwakI
3. Let it play for 10 sec
4. Pause it.
5. Notice the MBP's vent starts running in a while

I recorded a trace. There are a bunch of small tasks, 50us each, every 0.1ms.
The task attributes point to 

Title	TaskQueueManager::ProcessTaskFromWorkQueue
Category	toplevel
User Friendly Category	other
Start	
306.969 ms
Wall Duration	
0.053 ms
CPU Duration	
0.048 ms

Args
src_file	
"../../third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm"
src_func	
"startScrollbarPaintTimer"