Reset the signal vector at class construction time and check before emitting.
Reset the signal vector at class construction time and check before emitting.

This makes the implementation more robust and cleans up unit test warnings.

BUG=chromium-os:9815
TEST=unit tests, tested on device through dbus-monitor that the signals
are still emitted

Change-Id: I97797e157a9c7727992f0b713bf1996dae031de0

Review URL: http://codereview.chromium.org/6101004

chadversary/chromiumos.platform.login_manager,chadversary/chromiumos.platform.login_manager,joshfire/chromiumos-platform-login_manager,joshfire/chromiumos-platform-login_manager,chadversary/chromiumos.platform.login_manager,joshfire/chromiumos-platform-login_manager