Add platform methods to check reserved IP addresses.

This patch adds two methods to Platform which will allow us to improve
mixed content checking by determining whether SecurityOrigins and URLs
point to IP addresses that are reserved (e.g. 127.0.0.1, 192.168.0.1).

BUG=378566

Review URL: https://codereview.chromium.org/446363002

git-svn-id: svn://svn.chromium.org/blink/trunk@179719 bbb929c8-8fbe-4397-9dbb-9b2b20218538