wip - add dev_mix thing

Change-Id: Idc587424ff7620e628f6238e76f711d21115fa91
Revert ME! turn off audio_thread ut

Change-Id: I0baa66e2e6969e2d94fd0d9771c84a12c30b7258
CRAS: shm - shm argument to "frames_written" can be const.

Make this const since it isn't modified.  This will allow this
function to be called with a const shm pointer in a later change.

Change-Id: Ia998d921a87f14c7ff59afd18dde922bbce33263
Signed-off-by: Dylan Reid <dgreid@chromium.org>
wip: get input working with new timing