Cancel autoplay muted when visible if the video gets unmuted before being visible.

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 58f83cf70ca2b10351234242c41770ca26edb674..a6ce3a1aca4869adf9b9eee07e3114fdf3d8335c 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -2292,6 +2292,7 @@ void HTMLMediaElement::setMuted(bool muted)
         return;
 
     bool wasAutoplayingMuted = !paused() && m_muted && isLockedPendingUserGesture();
+    bool wasPendingAutoplayMuted = m_autoplayVisibilityObserver && paused() && m_muted && isLockedPendingUserGesture();
 
     if (UserGestureIndicator::processingUserGesture())
         unlockUserGesture();
@@ -2313,6 +2314,13 @@ void HTMLMediaElement::setMuted(bool muted)
             m_autoplayUmaHelper->recordAutoplayUnmuteStatus(AutoplayUnmuteActionStatus::Success);
         }
     }
+
+    // If an element was a candidate for autoplay muted but not visible, it will
+    // have a visibility observer ready to start its playback.
+    if (wasPendingAutoplayMuted) {
+        m_autoplayVisibilityObserver->stop();
+        m_autoplayVisibilityObserver = nullptr;
+    }
 }
 
 void HTMLMediaElement::updateVolume()