Monitor the intersection of video and viewport.

third_party/WebKit/Source/core/dom/IntersectionObservation.cpp

Index: third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
index c9c04457e5ea67c7f176de9f8542466870e0c392..cc44fa1532293b4640b71dacf076addaf603df25 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
@@ -19,7 +19,7 @@ IntersectionObservation::IntersectionObservation(IntersectionObserver& observer,
                                                  bool shouldReportRootBounds)

[miu, 2016/11/05 02:47:46]

Did you intend to remove the 3rd argument to this ctor? Otherwise, why are you
ignoring it now?

[xjz, 2016/11/09 02:24:28]

Now keep this argument for original purpose. 

     : m_observer(observer),
       m_target(&target),
-      m_shouldReportRootBounds(shouldReportRootBounds),
+      m_shouldReportRootBounds(true),
       m_lastThresholdIndex(0) {}
 
 void IntersectionObservation::applyRootMargin(LayoutRect& rect) const {
@@ -220,9 +220,9 @@ void IntersectionObservation::computeIntersectionObservations(
     float intersectionArea =
         geometry.intersectionRect.size().width().toFloat() *
         geometry.intersectionRect.size().height().toFloat();
-    float targetArea = geometry.targetRect.size().width().toFloat() *
-                       geometry.targetRect.size().height().toFloat();
-    newVisibleRatio = intersectionArea / targetArea;
+    float rootArea = geometry.rootRect.size().width().toFloat() *
+                     geometry.rootRect.size().height().toFloat();
+    newVisibleRatio = intersectionArea / rootArea;
     newThresholdIndex = observer().firstThresholdGreaterThan(newVisibleRatio);
   }
   if (m_lastThresholdIndex != newThresholdIndex) {