Delay back to back PulseAudio write request callbacks.
Avoids trampling shared memory when Pulse issues back to back
callbacks for whatever reason. Locally I hit the sleep many
times per stream without any noticeable glitching.
I've also adjusted the |minreq| value to reduce the number of
callbacks, in practice this shouldn't hurt buffering since we
always write out a full buffer regardless of the amount requested.
BUG=366433
TEST=pulse output is glitch free on WebAudio, HTML5, WebRTC.
Review URL: https://codereview.chromium.org/
414313005
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286955 0039d316-1c4b-4281-b951-d872f2087c98