chromeos_power: change some signals to methods

When libcros talks to powerd, it should use method_calls to avoid
broadcasting dbus signals to the whole system.

BUG=chromium-os:20115
TEST=none

Change-Id: Iecf16a9440eac4809267576eef2a218de6953b06
Signed-off-by: Simon Que <sque@chromium.org>
Reviewed-on: http://gerrit.chromium.org/gerrit/8094
Reviewed-by: Satoru Takabayashi <satorux@chromium.org>
2 files changed