DevTools: rename createAnchor into createExternalAnchor, use it instead of linkifyURLAsNode in some cases

BUG=

Review URL: https://codereview.chromium.org/677563003

git-svn-id: svn://svn.chromium.org/blink/trunk@184648 bbb929c8-8fbe-4397-9dbb-9b2b20218538