Make style independent of the presence of the <shadow> element.

BUG=353406
TEST=fast/dom/shadow/style-and-shadow-element.html

Review URL: https://codereview.chromium.org/210953003

git-svn-id: svn://svn.chromium.org/blink/trunk@170091 bbb929c8-8fbe-4397-9dbb-9b2b20218538