Fix an issue in fullscreen detector when context is destroyed

third_party/WebKit/Source/core/html/MediaCustomControlsFullscreenDetector.cpp

Index: third_party/WebKit/Source/core/html/MediaCustomControlsFullscreenDetector.cpp
diff --git a/third_party/WebKit/Source/core/html/MediaCustomControlsFullscreenDetector.cpp b/third_party/WebKit/Source/core/html/MediaCustomControlsFullscreenDetector.cpp
index 0d5a4ae6714079a8afe8222acc4ab629f142c4c5..39e9ee874369b1bcf003372bed0d6f83a6eba6a0 100644
--- a/third_party/WebKit/Source/core/html/MediaCustomControlsFullscreenDetector.cpp
+++ b/third_party/WebKit/Source/core/html/MediaCustomControlsFullscreenDetector.cpp
@@ -23,7 +23,6 @@ constexpr float kMostlyFillViewportThresholdOfVisibleProportion = 0.75f;
 MediaCustomControlsFullscreenDetector::MediaCustomControlsFullscreenDetector(
     HTMLVideoElement& video)
     : EventListener(CPPEventListenerType),
-      ContextLifecycleObserver(nullptr),
       m_videoElement(video),
       m_checkViewportIntersectionTimer(
           TaskRunnerHelper::get(TaskType::Unthrottled, &video.document()),
@@ -44,7 +43,6 @@ bool MediaCustomControlsFullscreenDetector::operator==(
 }
 
 void MediaCustomControlsFullscreenDetector::attach() {
-  setContext(&videoElement().document());
   videoElement().document().addEventListener(
       EventTypeNames::webkitfullscreenchange, this, true);
   videoElement().document().addEventListener(EventTypeNames::fullscreenchange,
@@ -52,12 +50,14 @@ void MediaCustomControlsFullscreenDetector::attach() {
 }
 
 void MediaCustomControlsFullscreenDetector::detach() {
-  setContext(nullptr);
   videoElement().document().removeEventListener(
       EventTypeNames::webkitfullscreenchange, this, true);
   videoElement().document().removeEventListener(
       EventTypeNames::fullscreenchange, this, true);
   m_checkViewportIntersectionTimer.stop();
+
+  if (videoElement().webMediaPlayer())
+    videoElement().webMediaPlayer()->setIsEffectivelyFullscreen(false);
 }
 
 bool MediaCustomControlsFullscreenDetector::computeIsDominantVideoForTests(
@@ -130,11 +130,11 @@ void MediaCustomControlsFullscreenDetector::handleEvent(
                                                 BLINK_FROM_HERE);
 }
 
-void MediaCustomControlsFullscreenDetector::contextDestroyed(
-    ExecutionContext*) {
-  if (videoElement().webMediaPlayer())
-    videoElement().webMediaPlayer()->setIsEffectivelyFullscreen(false);
-
+void MediaCustomControlsFullscreenDetector::contextDestroyed() {
+  // This method is called by HTMLVideoElement when it observes context destroy.
+  // The reason is that when HTMLMediaElement observes context destroy, it will
+  // destroy webMediaPlayer() thus the final setIsEffectivelyFullscreen(false)
+  // is not called.
   detach();
 }
 
@@ -164,7 +164,6 @@ bool MediaCustomControlsFullscreenDetector::isVideoOrParentFullscreen() {
 
 DEFINE_TRACE(MediaCustomControlsFullscreenDetector) {
   EventListener::trace(visitor);
-  ContextLifecycleObserver::trace(visitor);
   visitor->trace(m_videoElement);
 }