Reduce dependency on StyleResolver in StyleBuilderCustom

Also mark a couple of methods as const to allow a const RenderState
object to be used.

R=dglazkov@chromium.org
BUG=237268

Review URL: https://chromiumcodereview.appspot.com/18565006

git-svn-id: svn://svn.chromium.org/blink/trunk@154197 bbb929c8-8fbe-4397-9dbb-9b2b20218538