Make policy reloads explicit.
Make policy reloads explicit.

BUG=chromium-os:38541
TEST=unit tests pass
CQ-DEPEND=I20461078ca890c6ec2f81ad5383c06c4d75a64cd

Change-Id: I3f9ca593247816534d4f9f87e8a0c7db593b87b5
Reviewed-on: https://gerrit.chromium.org/gerrit/42540
Reviewed-by: Will Drewry <72416dde44ea762d19e3a7a555e3b59ce98f8eea@chromium.org>
Commit-Queue: Julian Pastarmov <c4978c99f3b8ea0c0f0653fba7cc0f598e925751@chromium.org>
Tested-by: Julian Pastarmov <c4978c99f3b8ea0c0f0653fba7cc0f598e925751@chromium.org>

endocode/update_engine,endocode/update_engine,marineam/update_engine,marineam/update_engine,mjg59/update_engine,endocode/update_engine,mjg59/update_engine,marineam/update_engine,mjg59/update_engine,marineam/update_engine