Web Audio: record autoplay status when an AudioContext is destroyed.

third_party/WebKit/Source/modules/webaudio/BaseAudioContext.cpp

Index: third_party/WebKit/Source/modules/webaudio/BaseAudioContext.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/BaseAudioContext.cpp b/third_party/WebKit/Source/modules/webaudio/BaseAudioContext.cpp
index a83ad8a0042c242a50b3ac384087e1e05eb993c2..69aefbf464652c6f8fe8c9901ddcf031cd6680ae 100644
--- a/third_party/WebKit/Source/modules/webaudio/BaseAudioContext.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/BaseAudioContext.cpp
@@ -108,6 +108,7 @@ BaseAudioContext::BaseAudioContext(Document* document)
   if (document->settings() &&
       document->settings()->mediaPlaybackRequiresUserGesture() &&
       document->frame() && document->frame()->isCrossOriginSubframe()) {
+    m_autoplayStatus = AutoplayStatus::AutoplayStatusFailed;
     m_userGestureRequired = true;
   }
 
@@ -145,6 +146,8 @@ BaseAudioContext::~BaseAudioContext() {
   DCHECK(!m_finishedSourceHandlers.size());
   DCHECK(!m_isResolvingResumePromises);
   DCHECK(!m_resumeResolvers.size());
+
+  recordAutoplayStatus();

[haraken, 2016/10/17 00:57:33]

This is safe but in general it's not encouraged to do something complicated in a
destructor.

Would there be any place other than the destructor to call
recordAutoplayStatus()?

[mlamouri (slow - plz ping), 2016/10/17 11:34:45]

I can call this in "uninitialize" which I did first with a DCHECH() in the dtor.
However, the DCHECK would get hit by some unit tests which makes me think that
"uninitialize" is only called in some circumstances.

The alternative is to record the histogram in uninitialize, reset the autoplay
status then record in dtor if the status is  set. However, I'm not sure it makes
this any better and makes the logic more complex and flaky.

WDYT?

 }
 
 void BaseAudioContext::initialize() {
@@ -562,6 +565,15 @@ PeriodicWave* BaseAudioContext::periodicWave(int type) {
   }
 }
 
+void BaseAudioContext::maybeRecordStartAttempt() {
+  if (!m_userGestureRequired || !UserGestureIndicator::processingUserGesture())
+    return;
+
+  DCHECK(!m_autoplayStatus.has_value() ||
+         m_autoplayStatus != AutoplayStatus::AutoplayStatusSucceeded);
+  m_autoplayStatus = AutoplayStatus::AutoplayStatusFailedWithStart;
+}
+
 String BaseAudioContext::state() const {
   // These strings had better match the strings for AudioContextState in
   // AudioContext.idl.
@@ -784,8 +796,12 @@ void BaseAudioContext::maybeUnlockUserGesture() {
   if (!m_userGestureRequired || !UserGestureIndicator::processingUserGesture())
     return;
 
+  DCHECK(!m_autoplayStatus.has_value() ||
+         m_autoplayStatus != AutoplayStatus::AutoplayStatusSucceeded);
+
   UserGestureIndicator::utilizeUserGesture();
   m_userGestureRequired = false;
+  m_autoplayStatus = AutoplayStatus::AutoplayStatusSucceeded;
 }
 
 bool BaseAudioContext::isAllowedToStart() const {
@@ -816,6 +832,18 @@ void BaseAudioContext::rejectPendingResolvers() {
   rejectPendingDecodeAudioDataResolvers();
 }
 
+void BaseAudioContext::recordAutoplayStatus() {
+  if (!m_autoplayStatus.has_value())
+    return;
+
+  DEFINE_STATIC_LOCAL(
+      EnumerationHistogram, autoplayHistogram,
+      ("WebAudio.Autoplay.CrossOrigin", AutoplayStatus::AutoplayStatusCount));
+  autoplayHistogram.count(m_autoplayStatus.value());
+
+  m_autoplayStatus.reset();
+}
+
 const AtomicString& BaseAudioContext::interfaceName() const {
   return EventTargetNames::AudioContext;
 }