DevTools: Correctly set DOM breakpoints on every target.

BUG=409857
R=pfeldman@chromium.org, sergeyv@chromium.org, dgozman@chromium.org

Review URL: https://codereview.chromium.org/535143003

git-svn-id: svn://svn.chromium.org/blink/trunk@181466 bbb929c8-8fbe-4397-9dbb-9b2b20218538