Broken by https://codereview.webrtc.org/2750783004/. Since samples are
two bytes each, only half of the buffer was being zeroed, leading to
garbage noise.
BUG=webrtc:7885,webrtc:7343
Change-Id: I46ecf90258b681ccdebbcfadd2e84ac6abadc9fe
Reviewed-on: https://chromium-review.googlesource.com/593092
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Jonathan Yu <yujo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#19194}