Include viewport visibility checks for autoplay experiment.

Source/core/html/HTMLMediaElement.h

Index: Source/core/html/HTMLMediaElement.h
diff --git a/Source/core/html/HTMLMediaElement.h b/Source/core/html/HTMLMediaElement.h
index a7362836febb0508e54c4cc3fba79efde6d46468..8e2f293754e03a93970b5fc7cce9a012f0ac6a5a 100644
--- a/Source/core/html/HTMLMediaElement.h
+++ b/Source/core/html/HTMLMediaElement.h
@@ -264,6 +264,9 @@ public:
     virtual bool isHTMLAudioElement() const { return false; }
     virtual bool isHTMLVideoElement() const { return false; }
 
+    // Temporary callback for crbug.com/487345,402044
+    void notifyPositionMayHaveChanged();
+
 protected:
     HTMLMediaElement(const QualifiedName&, Document&);
     ~HTMLMediaElement() override;
@@ -461,6 +464,9 @@ private:
 
     void audioTracksTimerFired(Timer<HTMLMediaElement>*);
 
+    // For tests.
+    void triggerAutoplayViewportCheck();
+
     Timer<HTMLMediaElement> m_loadTimer;
     Timer<HTMLMediaElement> m_progressEventTimer;
     Timer<HTMLMediaElement> m_playbackProgressTimer;