DevTools: Update LiveLocations whenever Sass UISourceCodes are added

BUG=260226
R=vsevik@chromium.org

Review URL: https://codereview.chromium.org/19173002

git-svn-id: svn://svn.chromium.org/blink/trunk@154283 bbb929c8-8fbe-4397-9dbb-9b2b20218538