bindings: Introduces type-check for the internal pointers.

Source/bindings/core/v8/CustomElementWrapper.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 83 matching lines @@
     v8::Handle<v8::Context> context = creationContext->CreationContext();
 
     if (!element->isUpgradedCustomElement() || DOMWrapperWorld::world(context).isIsolatedWorld())
         return createUpgradeCandidateWrapper(element.get(), creationContext, isolate, createSpecificWrapper);
 
     V8PerContextData* perContextData = V8PerContextData::from(context);
     if (!perContextData)
         return v8::Handle<v8::Object>();
 
     CustomElementBinding* binding = perContextData->customElementBinding(element->customElementDefinition());
-    v8::Handle<v8::Object> wrapper = V8DOMWrapper::createWrapper(creationContext, binding->wrapperType(), element.get(), isolate);
+    v8::Handle<v8::Object> wrapper = V8DOMWrapper::createWrapper(creationContext, binding->wrapperType(), WrapperType::toInternalPointer(element.get()), isolate);

[haraken, 2014/08/08 15:50:31]

What happens if someone passes element.get() to createWrapper or setNativeInfo
by mistake? I think we should have a way to detect the error. Would it be
possible to add ASSERTs to verify the following facts?

- Pointers stored into an internal field are internal pointers.
- Pointers retrieved from an internal field are internal pointers.

To verify the facts, probably you'll need to add a dummy member to something so
that the internal pointer and the head of the object have different addresses.
Adding such a dummy member is fine in Debug builds.

[Yuki, 2014/08/11 05:42:00]

Your idea sounds very nice and I'll add that check after
http://crrev.com/420233002 will be landed.

     if (wrapper.IsEmpty())
         return v8::Handle<v8::Object>();
 
     wrapper->SetPrototype(binding->prototype());
 
     V8DOMWrapper::associateObjectWithWrapper<WrapperType>(element, binding->wrapperType(), wrapper, isolate, WrapperConfiguration::Dependent);
     return wrapper;
 }
 
 template
 class CustomElementWrapper<HTMLElement, V8HTMLElement>;
 
 template
 class CustomElementWrapper<SVGElement, V8SVGElement>;
 
 } // namespace blink