GitLab

This will put the onus on individual observers to extract the security
information they require, after a change has occurred.  The intent is to
allow chrome/browser-residing observers to monitor security level
changes, independent of style.

BUG=641508

Review-Url: https://codereview.chromium.org/2562503002
Cr-Commit-Position: refs/heads/master@{#437659}