Simplify SelectorChecker's parentElement() function

Simplify SelectorChecker's parentElement() function by merging two if
conditions that end up returning the same result. This lets the compiler
generate slightly more efficient code.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/414453003

git-svn-id: svn://svn.chromium.org/blink/trunk@179399 bbb929c8-8fbe-4397-9dbb-9b2b20218538