When autoplaying muted video, record when unmute happen and the result.

third_party/WebKit/Source/core/html/HTMLMediaElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
index 59ec313479d5ee3100f21ca36dafafa2cc016bcf..ca61da61a790214102539ca6c915c2397ece8aa9 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -293,6 +293,13 @@ enum AutoplaySource {
     NumberOfAutoplaySources = 2,
 };
 
+// These values are used for histograms. Do not reorder.
+enum AutoplayUnmuteActionStatus {
+    AutoplayUnmuteActionFailure = 0,
+    AutoplayUnmuteActionSuccess = 1,
+    AutoplayUnmuteActionMax = 2,
+};
+
 } // anonymous namespace
 
 class HTMLMediaElement::AutoplayHelperClientImpl :
@@ -2292,9 +2299,6 @@ void HTMLMediaElement::setMuted(bool muted)
 {
     MEDIA_LOG << "setMuted(" << (void*)this << ", " << boolString(muted) << ")";
 
-    if (UserGestureIndicator::processingUserGesture())
-        unlockUserGesture();
-
     if (m_muted == muted)
         return;
 
@@ -2310,6 +2314,14 @@ void HTMLMediaElement::setMuted(bool muted)
 
     scheduleEvent(EventTypeNames::volumechange);
 
+    bool wasLocked = isGestureNeededForPlayback();

[whywhat, 2016/06/28 10:20:59]

nit: I think you either want:

bool wasLocked = m_lockedPendingUserGesture;

or

bool wasGestureNeededForPlayback = isGestureNeededForPlayback();

+    if (UserGestureIndicator::processingUserGesture())
+        unlockUserGesture();
+
+    // Record when unmuting a video that was autoplayed because it was muted.
+    if (wasLocked && !muted && isHTMLVideoElement() && RuntimeEnabledFeatures::autoplayMutedVideosEnabled())

[whywhat, 2016/06/28 10:20:59]

this condition seems to be very hard to read and maintain. Should've you checked
for data saver as well?

+        recordAutoplayUnmuteStatus(isGestureNeededForPlayback() ? AutoplayUnmuteStatus::Failure : AutoplayUnmuteStatus::Success);
+
     // Pause the element when unmuting if it's still locked.
     if (!muted && isGestureNeededForPlayback())

[whywhat, 2016/06/28 10:20:59]

// this implicitly relies on m_muted set to false beforehand, so I don't like it
much
// bool wasGestureNeededForPlayback = isGestureNeededForPlayback();

// this needs to be called at the top but at least the dependency is explicit
bool wasAutoplayingMuted = !paused() && m_muted && m_lockedPendingUserGesture;

// do other stuff, unlock the gesture if processing it
// ...

if (wasAutoplayingMuted) {
    if (isGestureNeededForPlayback())
        pause();
    recordAutoplayUnmutePausedState(paused());
}

wdyt?

         pause();
@@ -3890,6 +3902,13 @@ void HTMLMediaElement::recordAutoplaySourceMetric(int source)
     }
 }
 
+void HTMLMediaElement::recordAutoplayUnmuteStatus(AutoplayUnmuteStatus status)
+{
+    DEFINE_STATIC_LOCAL(EnumerationHistogram, autoplayUnmuteHistogram, ("Media.Video.Autoplay.Muted.UnmuteAction", AutoplayUnmuteActionMax));
+
+    autoplayUnmuteHistogram.count(status == AutoplayUnmuteStatus::Success ? AutoplayUnmuteActionSuccess : AutoplayUnmuteActionFailure);
+}
+
 void HTMLMediaElement::onVisibilityChangedForAutoplay(bool isVisible)
 {
     if (!isVisible)