CRAS: dbus - Use introspection for methods.
CRAS: dbus - Use introspection for methods.

Don't add matches for each method.  Instead use introspection to list the available methods.

BUG=none
TEST= use dbus-send to test each message:
dbus-send --system  --type=method_call --print-reply --dest=org.chromium.cras /org/chromium/cras/Control org.freedesktop.DBus.Introspectable.Introspect
dbus-send --system  --type=method_call --dest=org.chromium.cras /org/chromium/cras/Control org.chromium.cras.Control.SetSystemVolume byte:55
dbus-send --system  --type=method_call --dest=org.chromium.cras /org/chromium/cras/Control org.chromium.cras.Control.SetSystemCaptureGain int32:300
dbus-send --system  --type=method_call --dest=org.chromium.cras /org/chromium/cras/Control org.chromium.cras.Control.SetSystemCaptureMute boolean:true
dbus-send --system  --type=method_call --dest=org.chromium.cras /org/chromium/cras/Control org.chromium.cras.Control.SetSystemMute boolean:true
dbus-send --system --print-reply  --type=method_call --dest=org.chromium.cras /org/chromium/cras/Control org.chromium.cras.Control.GetSystemVolumeState

watch signals with "dbus-monitor --system"

Change-Id: Ia047818f4a59eca35ab8b9e5f0f5fe0d9102351f
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/44434

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