Remove PageVisibilityObserver contextDestroyed() notifications.

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

 /*
  * Copyright (C) 2004, 2006, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 154 matching lines @@
   bool shouldBeDirectComposited() const;
 
   void prepareSurfaceForPaintingIfNeeded() const;
 
   const AtomicString imageSourceURL() const override;
 
   InsertionNotificationRequest insertedInto(ContainerNode*) override;
 
   // ContextLifecycleObserver and PageVisibilityObserver implementation
   void contextDestroyed(ExecutionContext*) override;
-  void contextDestroyed(Page*) override;
 
   // PageVisibilityObserver implementation
   void pageVisibilityChanged() override;
 
   // CanvasImageSource implementation
   PassRefPtr<Image> getSourceImageForCanvas(SourceImageStatus*,
                                             AccelerationHint,
                                             SnapshotReason,
                                             const FloatSize&) const override;
   bool wouldTaintOrigin(SecurityOrigin*) const override;
@@ skipping 124 matching lines @@
   // Used for OffscreenCanvas that controls this HTML canvas element
   std::unique_ptr<CanvasSurfaceLayerBridge> m_surfaceLayerBridge;
 
   int m_numFramesSinceLastRenderingModeSwitch;
   bool m_pendingRenderingModeSwitch;
 };
 
 }  // namespace blink
 
 #endif  // HTMLCanvasElement_h