If a CSS animation which is offscreen is active, we tick the compositor thread at 60 fps even though nothing is changing on the screen. We do all the work necessary for producing a new frame and then early-out because nothing visible changed.

Example: http://output.jsbin.com/jutiriruke

Trace attached.
 

Deleted: trace_offscreen_css_anim.json.gz 2.2 MB

trace_offscreen_css_anim.json.gz 2.2 MB Download