DevTools: [SSP] consume event if it inserts a new property

Currently, if you click on the selector container, there are two
handlers that conflict with each other. The patch fixes
the conflict.

BUG=413894
R=vsevik, apavlov@chromium.org

Review URL: https://codereview.chromium.org/571653002

git-svn-id: svn://svn.chromium.org/blink/trunk@181963 bbb929c8-8fbe-4397-9dbb-9b2b20218538