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 bff62e7bfdb250473405fbd5bc2215a8d99b8bf2..1310d9cc440f55bc71606e7ddc4906c5ff3ae042 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -2290,12 +2290,14 @@ void HTMLMediaElement::setMuted(bool muted)
 {
     MEDIA_LOG << "setMuted(" << (void*)this << ", " << boolString(muted) << ")";
 
-    if (UserGestureIndicator::processingUserGesture())
-        unlockUserGesture();
-
     if (m_muted == muted)
         return;
 
+    bool wasAutoplayingMuted = !paused() && m_muted && isLockedPendingUserGesture();
+
+    if (UserGestureIndicator::processingUserGesture())

[whywhat, 2016/06/29 19:44:18]

nit: you could avoid moving that if calculating wasAutoplayingMuted above it.
Not sure though if it can happen that muted is changed with user gesture to the
same value and whether we should unlock the element in that case :) So perhaps
this move is okay.

[mlamouri (slow - plz ping), 2016/06/29 19:47:59]

ACK :)

+        unlockUserGesture();
+
     m_muted = muted;
     m_autoplayHelper->mutedChanged();
 
@@ -2308,9 +2310,16 @@ void HTMLMediaElement::setMuted(bool muted)
 
     scheduleEvent(EventTypeNames::volumechange);
 
-    // Pause the element when unmuting if it's still locked.
-    if (!muted && isGestureNeededForPlayback())
-        pause();
+    // If an element autoplayed while muted, it needs to be unlocked to unmute,
+    // otherwise, it will be paused.
+    if (wasAutoplayingMuted) {
+        if (isGestureNeededForPlayback()) {
+            pause();
+            recordAutoplayUnmuteStatus(AutoplayUnmuteActionFailure);
+        } else {
+            recordAutoplayUnmuteStatus(AutoplayUnmuteActionSuccess);
+        }
+    }
 }
 
 void HTMLMediaElement::updateVolume()
@@ -3898,6 +3907,13 @@ void HTMLMediaElement::recordAutoplaySourceMetric(int source)
     }
 }
 
+void HTMLMediaElement::recordAutoplayUnmuteStatus(AutoplayUnmuteActionStatus status)
+{
+    DEFINE_STATIC_LOCAL(EnumerationHistogram, autoplayUnmuteHistogram, ("Media.Video.Autoplay.Muted.UnmuteAction", AutoplayUnmuteActionMax));
+
+    autoplayUnmuteHistogram.count(status);
+}
+
 void HTMLMediaElement::onVisibilityChangedForAutoplay(bool isVisible)
 {
     if (!isVisible)