CSP: Add 'status-code' to violation reports.

A 'status-code' field has been added to CSP violation reports[1]; this
patch brings our implementation into line with the spec.

It also goes slightly beyond the spec by adding a 'statusCode' property
to the 'securitypolicyviolation' event, since they share a common data
structure in Blink. That seems like a reasonable addition that ought
to be proposed to the WebAppSec WG.

[1]: https://dvcs.w3.org/hg/content-security-policy/rev/ec76bd637141

R=abarth@chromium.org

Review URL: https://chromiumcodereview.appspot.com/18259019

git-svn-id: svn://svn.chromium.org/blink/trunk@154206 bbb929c8-8fbe-4397-9dbb-9b2b20218538