bindings: Introduces type-check for the internal pointers.

Source/bindings/core/v8/NPV8Object.cpp

Index: Source/bindings/core/v8/NPV8Object.cpp
diff --git a/Source/bindings/core/v8/NPV8Object.cpp b/Source/bindings/core/v8/NPV8Object.cpp
index 2713a73b59f37236f54110740957ca815beca5c5..c398d129e9b440839b77c9a11be5580264315834 100644
--- a/Source/bindings/core/v8/NPV8Object.cpp
+++ b/Source/bindings/core/v8/NPV8Object.cpp
@@ -112,7 +112,7 @@ static v8::Local<v8::String> npIdentifierToV8Identifier(NPIdentifier name, v8::I
 
 NPObject* v8ObjectToNPObject(v8::Handle<v8::Object> object)
 {
-    return reinterpret_cast<NPObject*>(object->GetAlignedPointerFromInternalField(v8DOMWrapperObjectIndex));
+    return reinterpret_cast<NPObject*>(toInternalPointer(object));
 }
 
 bool isWrappedNPObject(v8::Handle<v8::Object> object)
@@ -177,6 +177,11 @@ V8NPObject* npObjectToV8NPObject(NPObject* npObject)
     return v8NpObject;
 }
 
+ScriptWrappableBase* npObjectToInternalPointer(NPObject* npObject)
+{
+    return reinterpret_cast<ScriptWrappableBase*>(npObject);
+}
+
 void disposeUnderlyingV8Object(NPObject* npObject, v8::Isolate* isolate)
 {
     ASSERT(npObject);