Don't make RenderStyle::compare inline

This doesn't look like it needs to be inline, lets optimize it when we
cross that bridge.

R=eseidel@chromium.org,ojan@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23455043

git-svn-id: svn://svn.chromium.org/blink/trunk@157585 bbb929c8-8fbe-4397-9dbb-9b2b20218538