DevTools: [Elements] Do not copy nodes if there is a non-collapsed selection

This got regressed in r179031

R=aandrey, pfeldman
NOTRY=true

Review URL: https://codereview.chromium.org/413413003

git-svn-id: svn://svn.chromium.org/blink/trunk@179144 bbb929c8-8fbe-4397-9dbb-9b2b20218538