CSP source *.x.y should not match host x.y

      This fixes a minor CSP bug where a source in a source list with a
wildcard was matching more liberally than it should have. It was
matching a source of the form *.x.y to host x.y when, in fact, it should
only be matching subdomains.

BUG=534542
TBR=mkwst@chromium.org

Review URL: https://codereview.chromium.org/1367933003

Cr-Commit-Position: refs/heads/master@{#350629}