bindings: Introduces type-check for the internal pointers.

Source/bindings/core/v8/custom/V8MutationObserverCustom.cpp

Index: Source/bindings/core/v8/custom/V8MutationObserverCustom.cpp
diff --git a/Source/bindings/core/v8/custom/V8MutationObserverCustom.cpp b/Source/bindings/core/v8/custom/V8MutationObserverCustom.cpp
index 9c670c67dc5bceb105d8ec7ab81e644415ec3c6e..01462b8c15f7356384422f97a0092887825676d5 100644
--- a/Source/bindings/core/v8/custom/V8MutationObserverCustom.cpp
+++ b/Source/bindings/core/v8/custom/V8MutationObserverCustom.cpp
@@ -67,9 +67,9 @@ void V8MutationObserver::constructorCustom(const v8::FunctionCallbackInfo<v8::Va
     info.GetReturnValue().Set(wrapper);
 }
 
-void V8MutationObserver::visitDOMWrapper(void* object, const v8::Persistent<v8::Object>& wrapper, v8::Isolate* isolate)
+void V8MutationObserver::visitDOMWrapper(ScriptWrappableBase* internalPointer, const v8::Persistent<v8::Object>& wrapper, v8::Isolate* isolate)
 {
-    MutationObserver* observer = static_cast<MutationObserver*>(object);
+    MutationObserver* observer = fromInternalPointer(internalPointer);
     WillBeHeapHashSet<RawPtrWillBeMember<Node> > observedNodes = observer->getObservedNodes();
     for (WillBeHeapHashSet<RawPtrWillBeMember<Node> >::iterator it = observedNodes.begin(); it != observedNodes.end(); ++it) {
         v8::UniqueId id(reinterpret_cast<intptr_t>(V8GCController::opaqueRootForGC(*it, isolate)));