Revert 141476 - Do not stop audio physical stream immediately after logical one had stopped.

Wait some time.
We are still stopping/closing the stream, as (1) it is better for battery life,
and (2) some people can hear active device even when it is playing silence.

That increased audio startup latency, especially on Windows, because we are using 3
buffers on Windows. To fix that I changed the code to use 2 buffers on presumable
good Windows boxes -- i.e. running non-Vista and having more than single core.

Changed unit tests as well.

BUG=129190
TEST=Should not be noticeable difference in behavior. Run tests on Win7 and XP myself.

Review URL: https://chromiumcodereview.appspot.com/10540034

TBR=enal@chromium.org
Review URL: https://chromiumcodereview.appspot.com/10535117

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141505 0039d316-1c4b-4281-b951-d872f2087c98