Fix an issue in fullscreen detector when context is destroyed

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

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MediaCustomControlsFullscreenDetector_h
 #define MediaCustomControlsFullscreenDetector_h
 
 #include "core/CoreExport.h"
-#include "core/dom/ContextLifecycleObserver.h"
 #include "core/events/EventListener.h"
 #include "platform/Timer.h"
 
 namespace blink {
 
 class HTMLVideoElement;
 class IntRect;
 class TimerBase;
 
 class CORE_EXPORT MediaCustomControlsFullscreenDetector final
-    : public EventListener,
-      public ContextLifecycleObserver {
-  USING_GARBAGE_COLLECTED_MIXIN(MediaCustomControlsFullscreenDetector);
+    : public EventListener {
   WTF_MAKE_NONCOPYABLE(MediaCustomControlsFullscreenDetector);
 
  public:
   explicit MediaCustomControlsFullscreenDetector(HTMLVideoElement&);
 
   // EventListener implementation.
   bool operator==(const EventListener&) const override;
 
-  // ContextLifecycleObserver implemnetation.
-  void contextDestroyed(ExecutionContext*);
+  void contextDestroyed();
 
   DECLARE_VIRTUAL_TRACE();
 
  private:
   friend class MediaCustomControlsFullscreenDetectorTest;
   friend class HTMLMediaElementEventListenersTest;
 
   // EventListener implementation.
   void handleEvent(ExecutionContext*, Event*) override;
 
@@ skipping 12 matching lines @@
 
   // `m_videoElement` owns |this|.
   Member<HTMLVideoElement> m_videoElement;
   TaskRunnerTimer<MediaCustomControlsFullscreenDetector>
       m_checkViewportIntersectionTimer;
 };
 
 }  // namespace blink
 
 #endif  // MediaCustomControlsFullscreenDetector_h