Revert 138939 - alsa_output: Drain and pause pcm when stopping.

Revert 138939 - alsa_output: Drain and pause pcm when stopping.

Call snd_pcm_drain when the output's Stop() function is called.  This
will keep some alsa interfaces from repeating the last samples played
until Close() is called.  This will also guarantee that all samples are
played back if Close() is called immediately following Stop().

BUG=chromium-os:31211
TEST=Manual, play and pause youtube, both FLASH and HTML5 videos using
the following alsa plugins as a sink for alsa_output:  plug, hw, dmix,
pulse, cras, jack.  Observe that pauses are clean without repeated
samples.


Review URL: https://chromiumcodereview.appspot.com/10413075

TBR=dgreid@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=140538