DevTools: Highlight/select pseudo elements if hit in the searchingForNode mode

R=pfeldman, vsevik
BUG=301845

Review URL: https://codereview.chromium.org/25484003

git-svn-id: svn://svn.chromium.org/blink/trunk@158646 bbb929c8-8fbe-4397-9dbb-9b2b20218538