Detect change on the intersection of video and viewport.

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 a1f0ce6a74d593703d34135af4a59c9ecdc1652e..311186621cbf67ab19ced64c7c79d253418a6940 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -39,6 +39,7 @@
 #include "core/dom/ElementTraversal.h"
 #include "core/dom/ElementVisibilityObserver.h"
 #include "core/dom/Fullscreen.h"
+#include "core/dom/IntersectionGeometry.h"
 #include "core/dom/TaskRunnerHelper.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/events/Event.h"
@@ -2504,6 +2505,22 @@ void HTMLMediaElement::startPlaybackProgressTimer() {
 }
 
 void HTMLMediaElement::playbackProgressTimerFired(TimerBase*) {
+  if (m_webMediaPlayer) {
+    // Check whether the intersection with viewport has changed.
+    ExecutionContext* context = getExecutionContext();
+    DCHECK(context->isDocument());
+    Document& document = toDocument(*context);
+    IntersectionGeometry geometry(&document, this, Vector<Length>(), true);
+    geometry.computeGeometry();
+    WebRect intersectRect = geometry.intersectionIntRect();
+    if (m_currentViewportIntersection.intersectRect != intersectRect) {
+      m_currentViewportIntersection.intersectRect = intersectRect;
+      m_currentViewportIntersection.rootRect = geometry.rootIntRect();
+      m_webMediaPlayer->viewportIntersectionChanged(
+          m_currentViewportIntersection);
+    }
+  }
+
   if (!std::isnan(m_fragmentEndTime) && currentTime() >= m_fragmentEndTime &&
       getDirectionOfPlayback() == Forward) {
     m_fragmentEndTime = std::numeric_limits<double>::quiet_NaN();