bindings: Introduces type-check for the internal pointers.

Source/bindings/core/v8/CustomElementWrapper.cpp

Index: Source/bindings/core/v8/CustomElementWrapper.cpp
diff --git a/Source/bindings/core/v8/CustomElementWrapper.cpp b/Source/bindings/core/v8/CustomElementWrapper.cpp
index eaeb802e9836b9954b4cf5f18f60d32f59da91c2..1bc2625d9dd0ca917775452b4e6ad5d340ea1518 100644
--- a/Source/bindings/core/v8/CustomElementWrapper.cpp
+++ b/Source/bindings/core/v8/CustomElementWrapper.cpp
@@ -101,7 +101,7 @@ v8::Handle<v8::Object> CustomElementWrapper<ElementType, WrapperType>::wrap(Pass
         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>();