Use the invalidation tree walk for all class mutations, not just those that support
targeted style recalc.

This simplifies the code a bit and unifies the code paths.

BUG=335247
R=esprehn@chromium.org, ojan@chromium.org

Review URL: https://codereview.chromium.org/183583002

git-svn-id: svn://svn.chromium.org/blink/trunk@168175 bbb929c8-8fbe-4397-9dbb-9b2b20218538