Pretend the video has no audio track if it is playing as part of autoplay muted.

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

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights
  * reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 2335 matching lines @@
   return m_muted;
 }
 
 void HTMLMediaElement::setMuted(bool muted) {
   BLINK_MEDIA_LOG << "setMuted(" << (void*)this << ", " << boolString(muted)
                   << ")";
 
   if (m_muted == muted)
     return;
 
-  bool wasAutoplayingMuted =
-      !paused() && m_muted && isLockedPendingUserGesture();
+  bool wasAutoplayingMuted = isAutoplayingMuted();
   bool wasPendingAutoplayMuted = m_autoplayVisibilityObserver && paused() &&
                                  m_muted && isLockedPendingUserGesture();
 
   if (UserGestureIndicator::processingUserGesture())
     unlockUserGesture();
 
   m_muted = muted;
   m_autoplayHelper->mutedChanged();
 
-  updateVolume();
-
   scheduleEvent(EventTypeNames::volumechange);
 
   // If an element autoplayed while muted, it needs to be unlocked to unmute,
   // otherwise, it will be paused.
   if (wasAutoplayingMuted) {
     if (isGestureNeededForPlayback()) {
       pause();
       m_autoplayUmaHelper->recordAutoplayUnmuteStatus(
           AutoplayUnmuteActionStatus::Failure);
     } else {
       m_autoplayUmaHelper->recordAutoplayUnmuteStatus(
           AutoplayUnmuteActionStatus::Success);
     }
   }
 
+  // This is called after the volumechange event to make sure isAutoplayingMuted
+  // returns the right value when webMediaPlayer receives the volume update.
+  updateVolume();
+
   // 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() {
   if (webMediaPlayer())
@@ skipping 708 matching lines @@
     mediaControls()->stoppedCasting();
   if (remotePlaybackClient())
     remotePlaybackClient()->stateChanged(WebRemotePlaybackState::Disconnected);
 }
 
 void HTMLMediaElement::cancelledRemotePlaybackRequest() {
   if (remotePlaybackClient())
     remotePlaybackClient()->promptCancelled();
 }
 
+bool HTMLMediaElement::isAutoplayingMuted() {
+  if (!isHTMLVideoElement() ||
+      !RuntimeEnabledFeatures::autoplayMutedVideosEnabled()) {
+    return false;
+  }
+
+  return !paused() && muted() && isLockedPendingUserGesture();
+}
+
 void HTMLMediaElement::requestReload(const WebURL& newUrl) {
   DCHECK(webMediaPlayer());
   DCHECK(!m_srcObject);
   DCHECK(newUrl.isValid());
   DCHECK(isSafeToLoadURL(newUrl, Complain));
   resetMediaPlayerAndMediaSource();
   startPlayerLoad(newUrl);
 }
 
 // MediaPlayerPresentation methods
@@ skipping 970 matching lines @@
 
 IntRect HTMLMediaElement::AutoplayHelperClientImpl::absoluteBoundingBoxRect()
     const {
   IntRect result;
   if (LayoutObject* object = m_element->layoutObject())
     result = object->absoluteBoundingBoxRect();
   return result;
 }
 
 }  // namespace blink