OS: macOS 10.12.5

What steps will reproduce the problem?
(1) Cause an infobar to be displayed (e.g. launch a Chromium build without Google API keys).
(2) Cause the infobar to be dismissed (e.g. navigate to any page).

What is the expected result?
The infobar appears and disappears smoothly and uses minimal CPU.

What happens instead?
The infobar transition is expensive when Auto Layout is turned on, because (AFICT) each frame of the transition requires layout.

We should refactor the animation to use CA.