getViewportTopLeft: consider the new style "contain"
getViewportTopLeft: consider the new style "contain"

If an element's `contain` is/contains `paint`, then it will be forced
showing just as its `position` is `relative`.

philc/vimium,poacher2k/vimium,decaffeinate-examples/vimium,smblott-github/vimium,gdh1995/vimium,smblott-github/vimium,philc/vimium,gdh1995/vimium,poacher2k/vimium,gdh1995/vimium,mrmr1993/vimium,decaffeinate-examples/vimium,poacher2k/vimium,mrmr1993/vimium,smblott-github/vimium,decaffeinate-examples/vimium,mrmr1993/vimium,philc/vimium