create consent file for official builds

Once we get /etc/send_metrics in place on official builds, this change will notice and auto-create the consent file for metrics if it doesn't exist.

BUG=cros:1865
TEST=boot chromium os without /etc/send_metrics, see that no consent file is created.  create /etc/send_metrics and reboot...the consent file should now be present.

Review URL: http://codereview.chromium.org/1110003
1 file changed