DevTools: Move WebInspector.inspectedPage{URL,Domain} into ResourceTreeModel

R=eustas, pfeldman, vsevik
NOTRY=true

Review URL: https://codereview.chromium.org/196573010

git-svn-id: svn://svn.chromium.org/blink/trunk@169223 bbb929c8-8fbe-4397-9dbb-9b2b20218538