DevTools: [Elements] Restore selected shadow DOM elements on reload

R=pfeldman, vsevik
BUG=354853

Review URL: https://codereview.chromium.org/208223002

git-svn-id: svn://svn.chromium.org/blink/trunk@169842 bbb929c8-8fbe-4397-9dbb-9b2b20218538