コンポジタスレッドアーキテクチャ

https://www.chromium.org/developers/design-documents/compositor-thread-architecture

Goals The main render thread is a pretty scary place. This is where HTML, CSS, Javascript and pretty much everything on the web platform runs... or originates. It routinely stalls for tens to hundreds of milliseconds. On ARM, stalls can be seconds long. Sadly, it is not feasible to prevent all these stalls: style recalculation, synchronous network requests, long painting times, garbage collection, all these things have content-dependent costs.

The compositor thread architecture allows us to snapshot a version of the page and allow the user to scroll and see animations directly on the snapshot, presenting the illusion that the page is running smoothly.