Monitor the intersection of video and viewport.

third_party/WebKit/Source/core/dom/ElementVisibilityObserver.h

Index: third_party/WebKit/Source/core/dom/ElementVisibilityObserver.h
diff --git a/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.h b/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.h
index c048c2a84ef2acfe3147c12a03e784e2e8c25046..7e6eba6119df86da96ee5e366b4ba0dfea506746 100644
--- a/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.h
+++ b/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.h
@@ -34,10 +34,13 @@ class CORE_EXPORT ElementVisibilityObserver final
   virtual ~ElementVisibilityObserver();
 
   void start();
+  void start(const Vector<float>& thresholds);
   void stop();
 
   void deliverObservationsForTesting();
 
+  float ratio() { return m_ratio; }
+
   DECLARE_VIRTUAL_TRACE();
 
  private:
@@ -49,6 +52,7 @@ class CORE_EXPORT ElementVisibilityObserver final
   Member<Element> m_element;
   Member<IntersectionObserver> m_intersectionObserver;
   std::unique_ptr<VisibilityCallback> m_callback;
+  float m_ratio = 0;
 };
 
 }  // namespace blink