Implicit prefinalizer registration.

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 128 matching lines @@
 }
 
 DEFINE_NODE_FACTORY(HTMLCanvasElement)
 
 HTMLCanvasElement::~HTMLCanvasElement() {
   v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
       -m_externallyAllocatedMemory);
 }
 
 void HTMLCanvasElement::dispose() {
-  releasePlaceholderFrame();
+  if (placeholderFrame())
+    releasePlaceholderFrame();
 
   if (m_context) {
     m_context->detachCanvas();
     m_context = nullptr;
   }
 
   if (m_imageBuffer) {
     m_imageBuffer->setClient(nullptr);
     m_imageBuffer = nullptr;
   }
@@ skipping 1238 matching lines @@
   mojom::blink::OffscreenCanvasSurfacePtr service;
   Platform::current()->interfaceProvider()->getInterface(
       mojo::GetProxy(&service));
   m_surfaceLayerBridge =
       WTF::wrapUnique(new CanvasSurfaceLayerBridge(std::move(service)));
   return m_surfaceLayerBridge->createSurfaceLayer(this->width(),
                                                   this->height());
 }
 
 }  // namespace blink