Update target write period to 20ms in the desktop mixer.

This is analogous to the hardcoded value in the mixer used by the real
chromecast.

Bug: b/173016177
Change-Id: Ia1d2e779fe1ae74ee7cf824cabb4b1e18adfdc7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2538485
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Auto-Submit: Bryan Clark <bryanclark@google.com>
Cr-Commit-Position: refs/heads/master@{#827570}

chromecast/media/cma/backend/desktop/mixer_output_stream_desktop.cc

@@ -14,7 +14,7 @@ namespace chromecast {
 namespace media {
 
 constexpr base::TimeDelta kTargetWritePeriod =
-    base::TimeDelta::FromMilliseconds(10);
+    base::TimeDelta::FromMilliseconds(20);
 
 bool MixerOutputStreamDesktop::Start(int requested_sample_rate, int channels) {
   sample_rate_ = requested_sample_rate;