audio_widget: Add PlugHandler class to be used by CrosWidgetHandler

BUG=chromium:514541
TEST=not used yet.

Change-Id: Ifbabf97e4a42a8c2a8c0ae2f2f6664b92d6b8be1
Reviewed-on: https://chromium-review.googlesource.com/296244
Commit-Ready: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
1 file changed