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

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

 /*
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  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
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  * 1.  Redistributions of source code must retain the above copyright
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@@ skipping 90 matching lines @@
       m_closedContextSampleRate(-1),
       m_periodicWaveSine(nullptr),
       m_periodicWaveSquare(nullptr),
       m_periodicWaveSawtooth(nullptr),
       m_periodicWaveTriangle(nullptr) {
   // If mediaPlaybackRequiresUserGesture is enabled, cross origin iframes will
   // require user gesture for the AudioContext to produce sound.
   if (document->settings() &&
       document->settings()->mediaPlaybackRequiresUserGesture() &&
       document->frame() && document->frame()->isCrossOriginSubframe()) {
+    m_autoplayStatus = AutoplayStatus::AutoplayStatusFailed;
     m_userGestureRequired = true;
   }
 
   m_destinationNode = DefaultAudioDestinationNode::create(this);
 
   initialize();
 }
 
 // Constructor for offline (non-realtime) rendering.
 BaseAudioContext::BaseAudioContext(Document* document,
@@ skipping 17 matching lines @@
 
 BaseAudioContext::~BaseAudioContext() {
   deferredTaskHandler().contextWillBeDestroyed();
   // AudioNodes keep a reference to their context, so there should be no way to
   // be in the destructor if there are still AudioNodes around.
   DCHECK(!isDestinationInitialized());
   DCHECK(!m_activeSourceNodes.size());
   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() {
   if (isDestinationInitialized())
     return;
 
   FFTFrame::initialize();
 
   if (m_destinationNode) {
     m_destinationNode->handler().initialize();
@@ skipping 397 matching lines @@
       // Initialize the table if necessary
       if (!m_periodicWaveTriangle)
         m_periodicWaveTriangle = PeriodicWave::createTriangle(sampleRate());
       return m_periodicWaveTriangle;
     default:
       NOTREACHED();
       return nullptr;
   }
 }
 
+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.
   switch (m_contextState) {
     case Suspended:
       return "suspended";
     case Running:
       return "running";
     case Closed:
       return "closed";
@@ skipping 202 matching lines @@
   for (auto& resolver : m_decodeAudioResolvers)
     resolver->reject(
         DOMException::create(InvalidStateError, "Audio context is going away"));
   m_decodeAudioResolvers.clear();
 }
 
 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 {
   if (!m_userGestureRequired)
     return true;
 
   toDocument(getExecutionContext())
       ->addConsoleMessage(ConsoleMessage::create(
           JSMessageSource, WarningMessageLevel,
           "An AudioContext in a cross origin iframe must be created or resumed "
@@ skipping 10 matching lines @@
   for (auto& resolver : m_resumeResolvers) {
     resolver->reject(
         DOMException::create(InvalidStateError, "Audio context is going away"));
   }
   m_resumeResolvers.clear();
   m_isResolvingResumePromises = false;
 
   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;
 }
 
 ExecutionContext* BaseAudioContext::getExecutionContext() const {
   return ActiveDOMObject::getExecutionContext();
 }
 
 void BaseAudioContext::startRendering() {
   // This is called for both online and offline contexts.
@@ skipping 23 matching lines @@
 }
 
 SecurityOrigin* BaseAudioContext::getSecurityOrigin() const {
   if (getExecutionContext())
     return getExecutionContext()->getSecurityOrigin();
 
   return nullptr;
 }
 
 }  // namespace blink