cocoa browser: add accessible tooltip for security state

The accessible tooltip is: "Label text. View site information, button", where
the label text is either "Secure" for regular SSL sites, or the origin's EV
name for EV sites.

BUG=447191

Review-Url: https://codereview.chromium.org/2407853002
Cr-Commit-Position: refs/heads/master@{#424155}
2 files changed