chameleon_audio_helper: Add usb_facade to AudioWidgetFactory

usb_facade is a USBFacadeRemoteAdapter object that will be needed
for Cros devices with USB ports to implement its Plug and Unplug.

BUG=chromium:514541
TEST=not used yet.

Change-Id: I22de1c31a5f6de20a49c0b4be65794038072873b
Reviewed-on: https://chromium-review.googlesource.com/296243
Commit-Ready: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
diff --git a/client/cros/chameleon/chameleon_audio_helper.py b/client/cros/chameleon/chameleon_audio_helper.py
index 3a02015..a5825b9 100644
--- a/client/cros/chameleon/chameleon_audio_helper.py
+++ b/client/cros/chameleon/chameleon_audio_helper.py
@@ -225,6 +225,7 @@
 
         """
         self._audio_facade = factory.create_audio_facade()
+        self._usb_facade = factory.create_usb_facade()
         self._cros_host = cros_host
         self._chameleon_board = cros_host.chameleon
         self._link_factory = AudioLinkFactory(cros_host)