Add metrics for AudioContextOptions.latencyHint

Add metrics to record the value of latencyHint which can be one of
four values in the following order:

  "interactive"
  "balanced"
  "playback"
  exact

The first three are the values of the AudioContextLatencyCatergory
enum.  The last is for case when an explicit floating-point value
is given.

When the hint is a floating-point value, we record the value in
milliseconds.

Each of these metrics are recorded each time an AudioContext is
created.

Bug: 1156304
Change-Id: I264f6f9a38983bd0e40f42e720cfcf685e7a1cdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586047Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836777}

content/renderer/media/renderer_webaudiodevice_impl.cc

@@ -48,6 +48,8 @@ blink::WebAudioDeviceSourceType GetLatencyHintSourceType(
       return blink::WebAudioDeviceSourceType::kWebAudioPlayback;
     case WebAudioLatencyHint::kCategoryExact:
       return blink::WebAudioDeviceSourceType::kWebAudioExact;
+    case WebAudioLatencyHint::kLastValue:
+      NOTREACHED();
   }
   NOTREACHED();
   return blink::WebAudioDeviceSourceType::kWebAudioInteractive;

third_party/blink/public/platform/web_audio_latency_hint.h

@@ -17,7 +17,8 @@ class WebAudioLatencyHint {
     kCategoryInteractive,
     kCategoryBalanced,
     kCategoryPlayback,
-    kCategoryExact
+    kCategoryExact,
+    kLastValue
   };
 
   explicit WebAudioLatencyHint(const WebString& category) {

third_party/blink/renderer/modules/webaudio/audio_context.cc

@@ -74,8 +74,16 @@ AudioContext* AudioContext::Create(Document& document,
     // into account double buffering (same as baseLatency).
     latency_hint =
         WebAudioLatencyHint(context_options->latencyHint().GetAsDouble());
+
+    base::UmaHistogramTimes(
+        "WebAudio.AudioContext.latencyHintMilliSeconds",
+        base::TimeDelta::FromSecondsD(latency_hint.Seconds()));
   }
 
+  base::UmaHistogramEnumeration(
+      "WebAudio.AudioContext.latencyHintCategory", latency_hint.Category(),
+      WebAudioLatencyHint::AudioContextLatencyCategory::kLastValue);
+
   base::Optional<float> sample_rate;
   if (context_options->hasSampleRate()) {
     sample_rate = context_options->sampleRate();

tools/metrics/histograms/histograms_xml/web_audio/histograms.xml

@@ -72,6 +72,30 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="WebAudio.AudioContext.latencyHintCategory" units="units"
+    expires_after="2021-06-30">
+  <owner>rtoy@chromium.org</owner>
+  <owner>hongchan@chromium.org</owner>
+  <summary>
+    If provided, the latencyHint option category of &quot;interactive&quot;,
+    &quot;balanced&quot;, &quot;playback&quot;, or &quot;exact&quot;, in that
+    order where &quot;exact&quot; means an explicit floating point value was
+    provided. Recorded for every AudioContext that is constructed with a
+    latencyHint.
+  </summary>
+</histogram>
+
+<histogram name="WebAudio.AudioContext.latencyHintMilliSeconds" units="ms"
+    expires_after="2021-06-30">
+  <owner>rtoy@chromium.org</owner>
+  <owner>hongchan@chromium.org</owner>
+  <summary>
+    If the latencyHint is provided and is a floating-point number, the value in
+    milliseconds is recorded. This is recorded for every AudioContext that is
+    constructed with a floating-point latencyHint value.
+  </summary>
+</histogram>
+
 <histogram name="WebAudio.AudioContext.MaxChannelsAvailable" units="units"
     expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>