Does Game Closure provide / require you to use its own game engine, or just provide a canvas-compatible rendering context?

I'm trying to improve performance of my ImpactJS-based game on Android, but none of the other canvas reimplementations I've played with (e.g. Cocoon, Crosswalk) are meaningfully more performant than a regular old web view.

If Game Closure will let me drop my existing canvas-based game into an optimized canvas context, a la Ejecta on iOS, I'd be super interested in checking it out. The docs are making it hard for me to figure out what it actually provides.