Start autoplay muted videos with autoplay attribute when they are 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 d77204149ea63e355658a4ac626326305a7e18e0..be8b21a65531439b946a5e2399f93afb5c7e130a 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -35,6 +35,7 @@
 #include "core/dom/Attribute.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/ElementTraversal.h"
+#include "core/dom/ElementVisibilityObserver.h"
 #include "core/dom/Fullscreen.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/events/Event.h"
@@ -354,7 +355,6 @@ private:
     Member<HTMLMediaElement> m_element;
 };
 
-
 void HTMLMediaElement::recordAutoplayMetric(AutoplayMetrics metric)
 {
     DEFINE_STATIC_LOCAL(EnumerationHistogram, autoplayHistogram, ("Blink.MediaElement.Autoplay", NumberOfAutoplayMetrics));
@@ -1641,16 +1641,20 @@ void HTMLMediaElement::setReadyState(ReadyState state)
         // Check for autoplay, and record metrics about it if needed.
         if (shouldAutoplay(RecordMetricsBehavior::DoRecord)) {
             recordAutoplaySourceMetric(AutoplaySourceAttribute);
-            // If the autoplay experiment says that it's okay to play now,
-            // then don't require a user gesture.
+
             m_autoplayHelper->becameReadyToPlay();
 
             if (!isGestureNeededForPlayback()) {
-                m_paused = false;
-                invalidateCachedTime();
-                scheduleEvent(EventTypeNames::play);
-                scheduleNotifyPlaying();
-                m_autoplaying = false;
+                if (muted() && RuntimeEnabledFeatures::autoplayMutedVideosEnabled()) {
+                    m_autoplayVisibilityObserver = new ElementVisibilityObserver(this, WTF::bind<bool>(&HTMLMediaElement::visibilityChangedForAutoplay, this));
+                    m_autoplayVisibilityObserver->start();
+                } else {
+                    m_paused = false;
+                    invalidateCachedTime();
+                    scheduleEvent(EventTypeNames::play);
+                    scheduleNotifyPlaying();
+                    m_autoplaying = false;
+                }
             }
         }
 
@@ -3641,6 +3645,7 @@ DEFINE_TRACE(HTMLMediaElement)
     visitor->trace(m_autoplayHelperClient);
     visitor->trace(m_autoplayHelper);
     visitor->trace(m_srcObject);
+    visitor->trace(m_autoplayVisibilityObserver);
     visitor->template registerWeakMembers<HTMLMediaElement, &HTMLMediaElement::clearWeakMembers>(this);
     Supplementable<HTMLMediaElement>::trace(visitor);
     HTMLElement::trace(visitor);
@@ -3853,6 +3858,15 @@ void HTMLMediaElement::recordAutoplaySourceMetric(int source)
     }
 }
 
+void HTMLMediaElement::visibilityChangedForAutoplay(bool visibility) {
+    if (!visibility)
+      return;
+
+    playInternal();
+    m_autoplayVisibilityObserver->stop();
+    m_autoplayVisibilityObserver = nullptr;
+}
+
 void HTMLMediaElement::clearWeakMembers(Visitor* visitor)
 {
     if (!ThreadHeap::isHeapObjectAlive(m_audioSourceNode)) {