Fix examine page on builder/master alerts.

r183235 removed the url property on the builder/master failure-group-datas,
which is how the examine page knows what iframe to show.

TBR=leviw@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/627333002

git-svn-id: svn://svn.chromium.org/blink/trunk@183239 bbb929c8-8fbe-4397-9dbb-9b2b20218538