Simplify Node::invalidateNodeListCachesInAncestors()'s code a bit

Simplify Node::invalidateNodeListCachesInAncestors()'s code a bit by re-using
Node::nodeLists() getter instead of duplicating its implementation.

R=adamk, abarth

Review URL: https://codereview.chromium.org/158093003

git-svn-id: svn://svn.chromium.org/blink/trunk@166786 bbb929c8-8fbe-4397-9dbb-9b2b20218538