Adds CookieManager methods to configure policy for cookies for file scheme URLs

Needs https://android-git.corp.google.com/g/83647 in external/webkit,
which disallows such cookies by default and provides configuration
methods native side.

Also updates TestShellActivity to allow such cookies, as they are
required for the page cycler.

Bug: 2944150
Change-Id: Idcc7e2812fab33e6a2a8766a2176bc3278e617da