DevTools overlay: use screen, not page coords when passing highlight shapes

This seems to cut a few lines and makes things a bit simpler.

BUG=

Review URL: https://codereview.chromium.org/406203002

git-svn-id: svn://svn.chromium.org/blink/trunk@178914 bbb929c8-8fbe-4397-9dbb-9b2b20218538