As one of ShadowDOM performance benchmark suite, we would like to have micro benchmarks in PerformanceTest of WebKit. See also: https://docs.google.com/a/chromium.org/document/d/1bl451Q6Hmf01r6fl07I_zF0fSsq8OJW70HPKMwZpvuI/edit#
Not gonna do this anytime soon.