Make the metrics library respect the policy settings instead of the consent file.

BUG=chromium-os:17012
TEST=metrics_library_test

This is a second try at committing http://gerrit.chromium.org/gerrit/#change,3865

Change-Id: I8c874ca26dd0d07471cfc66ded527ad5c3a1cd20
Reviewed-on: http://gerrit.chromium.org/gerrit/4578


Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Tested-by: Julian Pastarmov <pastarmovj@chromium.org>