Implement autoplay gesture override experiment.

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index 63eda2639e62a01ca9a5fd97b8bdfc5a2bd153f8..9360e955c7a83c5df89de8c3fcf6baf1d3586da3 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -251,25 +251,7 @@ static bool canLoadURL(const KURL& url, const ContentType& contentType, const St
     return false;
 }
 
-// These values are used for a histogram. Do not reorder.
-enum AutoplayMetrics {
-    // Media element with autoplay seen.
-    AutoplayMediaFound = 0,
-    // Autoplay enabled and user stopped media play at any point.
-    AutoplayStopped = 1,
-    // Autoplay enabled but user bailed out on media play early.
-    AutoplayBailout = 2,
-    // Autoplay disabled but user manually started media.
-    AutoplayManualStart = 3,
-    // Autoplay was (re)enabled through a user-gesture triggered load()
-    AutoplayEnabledThroughLoad = 4,
-    // Autoplay disabled by sandbox flags.
-    AutoplayDisabledBySandbox = 5,
-    // This enum value must be last.
-    NumberOfAutoplayMetrics,
-};
-
-static void recordAutoplayMetric(AutoplayMetrics metric)
+void HTMLMediaElement::recordAutoplayMetric(AutoplayMetrics metric)
 {
     Platform::current()->histogramEnumeration("Blink.MediaElement.Autoplay", metric, NumberOfAutoplayMetrics);
 }
@@ -367,6 +349,7 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName, Document& docum
 #if ENABLE(WEB_AUDIO)
     , m_audioSourceNode(nullptr)
 #endif
+    , m_autoplayHelper(*this)
 {
 #if ENABLE(OILPAN)
     ThreadState::current()->registerPreFinalizer(this);
@@ -385,6 +368,7 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName, Document& docum
 HTMLMediaElement::~HTMLMediaElement()
 {
     WTF_LOG(Media, "HTMLMediaElement::~HTMLMediaElement(%p)", this);
+
 #if !ENABLE(OILPAN)
     // HTMLMediaElement and m_asyncEventQueue always become unreachable
     // together. So HTMLMediaElement and m_asyncEventQueue are destructed in
@@ -694,12 +678,37 @@ String HTMLMediaElement::canPlayType(const String& mimeType, const String& keySy
     return canPlay;
 }
 
+void HTMLMediaElement::recordMetricsIfStopping()

[philipj_slow, 2015/08/13 11:12:48]

Since this AutoplayExperimentHelper is a friend class, can't this and basically
everything except a few callbacks be moved there? isBailout() doesn't even need
any internal state.

[liberato (no reviews please), 2015/09/01 06:54:20]

they could, but they were part of the old autoplay experiment as well.  when we
remove the new one, i don't know if we'll also want to remove the old one.

+{
+    // If not playing, then nothing to record.
+    if (!m_playing)
+        return;
+
+    const bool bailout = isBailout();
+
+    // Record that play was stopped.  We don't care if it was autoplay,
+    // play(), or the user manually started it.
+    recordAutoplayMetric(AnyPlaybackStopped);
+    if (bailout)
+        recordAutoplayMetric(AnyPlaybackBailout);
+
+    // If this was a gestureless play, then record that separately.
+    // These cover attr and play() gestureless starts.
+    if (m_initialPlayWithoutUserGestures) {
+        m_initialPlayWithoutUserGestures = false;
+
+        recordAutoplayMetric(AutoplayStopped);
+
+        if (bailout)
+            recordAutoplayMetric(AutoplayBailout);
+    }
+}
+
 void HTMLMediaElement::load()
 {
     WTF_LOG(Media, "HTMLMediaElement::load(%p)", this);
 
-    if (m_initialPlayWithoutUserGestures && m_playing)
-        gesturelessInitialPlayHalted();
+    recordMetricsIfStopping();
 
     if (UserGestureIndicator::processingUserGesture() && m_userGestureRequiredForPlay) {
         recordAutoplayMetric(AutoplayEnabledThroughLoad);
@@ -1555,11 +1564,17 @@ void HTMLMediaElement::setReadyState(ReadyState state)
 
             if (document().isSandboxed(SandboxAutomaticFeatures)) {
                 recordAutoplayMetric(AutoplayDisabledBySandbox);
-            } else if (!m_userGestureRequiredForPlay) {
-                m_paused = false;
-                invalidateCachedTime();
-                scheduleEvent(EventTypeNames::play);
-                scheduleEvent(EventTypeNames::playing);
+            } else {
+                // If the autoplay experiment says that it's okay to play now,
+                // then don't require a user gesture.
+                m_autoplayHelper.onReadyToPlay();
+
+                if (!m_userGestureRequiredForPlay) {
+                    m_paused = false;
+                    invalidateCachedTime();
+                    scheduleEvent(EventTypeNames::play);
+                    scheduleEvent(EventTypeNames::playing);
+                }
             }
         }
 
@@ -1960,9 +1975,13 @@ void HTMLMediaElement::play()
 {
     WTF_LOG(Media, "HTMLMediaElement::play(%p)", this);
 
+    m_autoplayHelper.onPlayMethodCalled();
+
     if (!UserGestureIndicator::processingUserGesture()) {
         autoplayMediaEncountered();
+
         if (m_userGestureRequiredForPlay) {
+            recordAutoplayMetric(PlayMethodFailed);

[philipj_slow, 2015/08/13 11:12:48]

If recordAutoplayMetric is also moved to the helper, I guess replace this with a
callback.

[liberato (no reviews please), 2015/09/01 06:54:20]

Acknowledged.

             String message = ExceptionMessages::failedToExecute("play", "HTMLMediaElement", "API can only be initiated by a user gesture.");
             document().executionContext()->addConsoleMessage(ConsoleMessage::create(JSMessageSource, WarningMessageLevel, message));
             return;
@@ -2020,21 +2039,13 @@ void HTMLMediaElement::autoplayMediaEncountered()
     }
 }
 
-void HTMLMediaElement::gesturelessInitialPlayHalted()
+bool HTMLMediaElement::isBailout() const
 {
-    ASSERT(m_initialPlayWithoutUserGestures);
-    m_initialPlayWithoutUserGestures = false;
-
-    recordAutoplayMetric(AutoplayStopped);
-
     // We count the user as having bailed-out on the video if they watched
     // less than one minute and less than 50% of it.
-    double playedTime = currentTime();
-    if (playedTime < 60) {
-        double progress = playedTime / duration();
-        if (progress < 0.5)
-            recordAutoplayMetric(AutoplayBailout);
-    }
+    const double playedTime = currentTime();
+    const double progress = playedTime / duration();
+    return (playedTime < 60) && (progress < 0.5);
 }
 
 void HTMLMediaElement::pause()
@@ -2044,11 +2055,12 @@ void HTMLMediaElement::pause()
     if (m_networkState == NETWORK_EMPTY)
         scheduleDelayedAction(LoadMediaResource);
 
+    m_autoplayHelper.onPauseMethodCalled();
+
     m_autoplaying = false;
 
     if (!m_paused) {
-        if (m_initialPlayWithoutUserGestures)
-            gesturelessInitialPlayHalted();
+        recordMetricsIfStopping();
 
         m_paused = true;
         scheduleTimeupdateEvent(false);
@@ -2141,6 +2153,8 @@ void HTMLMediaElement::setMuted(bool muted)
 
     m_muted = muted;
 
+    m_autoplayHelper.onMuteChanged();

[philipj_slow, 2015/08/13 11:12:48]

s/Mute/Muted/

[liberato (no reviews please), 2015/09/01 06:54:20]

Done.

+
     updateVolume();
 
     scheduleEvent(EventTypeNames::volumechange);
@@ -2772,6 +2786,7 @@ void HTMLMediaElement::timeChanged()
                 m_sentEndEvent = true;
                 scheduleEvent(EventTypeNames::ended);
             }
+            recordMetricsIfStopping();
             // If the media element has a current media controller, then report the controller state
             // for the media element's current media controller.
             updateMediaController();
@@ -2992,6 +3007,7 @@ void HTMLMediaElement::updatePlayState()
             mediaControls()->playbackStarted();
         startPlaybackProgressTimer();
         m_playing = true;
+        recordAutoplayMetric(AnyPlaybackStarted);
 
     } else { // Should not be playing right now
         if (isPlaying)
@@ -3111,8 +3127,7 @@ void HTMLMediaElement::stop()
 {
     WTF_LOG(Media, "HTMLMediaElement::stop(%p)", this);
 
-    if (m_playing && m_initialPlayWithoutUserGestures)
-        gesturelessInitialPlayHalted();
+    recordMetricsIfStopping();

[philipj_slow, 2015/08/13 11:12:48]

HTMLMediaElement::stop() is an ActiveDOMObject override, I don't think it
actually makes sense to include this in the metrics, not sure why it was done
originally. In order to capture cases where users close the tab in reaction to
autoplay, it would be better measured somewhere else explicitly, I think.

[philipj_slow, 2015/09/02 09:31:47]

Ping.

 
     // Close the async event queue so that no events are enqueued by userCancelledLoad.
     cancelPendingEventsAndCallbacks();
@@ -3721,6 +3736,21 @@ void HTMLMediaElement::selectInitialTracksIfNecessary()
         videoTracks().anonymousIndexedGetter(0)->setSelected(true);
 }
 
+bool HTMLMediaElement::isUserGestureRequiredForPlay() const
+{
+    return m_userGestureRequiredForPlay;
+}
+
+void HTMLMediaElement::removeUserGestureRequirement()
+{
+    m_userGestureRequiredForPlay = false;
+}
+
+void HTMLMediaElement::setInitialPlayWithoutUserGestures(bool value)
+{
+    m_initialPlayWithoutUserGestures = value;

[philipj_slow, 2015/08/13 11:12:48]

You didn't add m_initialPlayWithoutUserGestures, but if you want to rename it to
m_initialPlayWithoutUserGesture that'd be nice. The plural doesn't make sense to
me.

[liberato (no reviews please), 2015/09/01 06:54:20]

Done.

+}
+
 #if ENABLE(WEB_AUDIO)
 void HTMLMediaElement::clearWeakMembers(Visitor* visitor)
 {