Add DynamicAudioTimeout Feature

This CL adds an off-by-default feature flag, used to experiment with
audio rendering timeouts, on all platforms other than Mac and CrOS.

When the feature is turned on, the audio timeout is set to half
a buffer's duration, rather than the 20ms default. The 20ms default was
historically needed to prevent issues on versions of WinXP and such.

This feature will be gradually rolled out via finch, and we will
measure its effects by observing audio glitch metrics.

Bug: 1244531
Change-Id: Ie5fd1d26c783e3f32d4bcd8ef7d1c42c465f376e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3138468
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Auto-Submit: Thomas Guilbert <tguilbert@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#917498}

services/audio/sync_reader.cc

@@ -41,6 +41,12 @@ void LogAudioGlitchResult(AudioGlitchResult result) {
 
 namespace audio {
 
+#if !defined(OS_MAC) && !BUILDFLAG(IS_CHROMEOS_ASH) && \
+    !BUILDFLAG(IS_CHROMEOS_LACROS)
+const base::Feature kDynamicAudioTimeout{"DynamicAudioTimeout",
+                                         base::FEATURE_DISABLED_BY_DEFAULT};
+#endif
+
 SyncReader::SyncReader(
     base::RepeatingCallback<void(const std::string&)> log_callback,
     const media::AudioParameters& params,
@@ -55,14 +61,18 @@ SyncReader::SyncReader(
       renderer_callback_count_(0),
       renderer_missed_callback_count_(0),
       trailing_renderer_missed_callback_count_(0),
+      buffer_index_(0) {
 #if defined(OS_MAC) || BUILDFLAG(IS_CHROMEOS_ASH) || \
     BUILDFLAG(IS_CHROMEOS_LACROS)
-      maximum_wait_time_(params.GetBufferDuration() / 2),
+  maximum_wait_time_ = params.GetBufferDuration() / 2;
 #else
-      // TODO(dalecurtis): Investigate if we can reduce this on all platforms.
-      maximum_wait_time_(base::TimeDelta::FromMilliseconds(20)),
+  if (base::FeatureList::IsEnabled(kDynamicAudioTimeout)) {
+    maximum_wait_time_ = params.GetBufferDuration() / 2;
+  } else {
+    maximum_wait_time_ = base::TimeDelta::FromMilliseconds(20);
+  }
 #endif
-      buffer_index_(0) {
+
   base::CheckedNumeric<size_t> memory_size =
       media::ComputeAudioOutputBufferSizeChecked(params);
   if (!memory_size.IsValid())