Revert "Remove redundant checks from SharedStyleFinder::canShareStyleWithElement"

This reverts commit 481c9bfa6a21d9f1bcf9610820e2465c02c76173.

BUG=310266
TBR=esprehn@chromium.org,eseidel@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/34623006

git-svn-id: svn://svn.chromium.org/blink/trunk@160248 bbb929c8-8fbe-4397-9dbb-9b2b20218538