Remove PageVisibilityObserver contextDestroyed() notifications.

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

 /*
  * Copyright (C) 2004, 2006, 2007 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 1184 matching lines @@
       discardImageBuffer();
     }
   }
 }
 
 void HTMLCanvasElement::contextDestroyed(ExecutionContext*) {
   if (m_context)
     m_context->stop();
 }
 
-void HTMLCanvasElement::contextDestroyed(Page*) {}
-
 void HTMLCanvasElement::styleDidChange(const ComputedStyle* oldStyle,
                                        const ComputedStyle& newStyle) {
   if (m_context)
     m_context->styleDidChange(oldStyle, newStyle);
 }
 
 void HTMLCanvasElement::didMoveToNewDocument(Document& oldDocument) {
   ContextLifecycleObserver::setContext(&document());
   PageVisibilityObserver::setContext(document().page());
   HTMLElement::didMoveToNewDocument(oldDocument);
@@ skipping 199 matching lines @@
   m_surfaceLayerBridge = WTF::wrapUnique(new CanvasSurfaceLayerBridge(this));
   // Creates a placeholder layer first before Surface is created.
   m_surfaceLayerBridge->createSolidColorLayer();
 }
 
 void HTMLCanvasElement::OnWebLayerReplaced() {
   setNeedsCompositingUpdate();
 }
 
 }  // namespace blink