bindings: Introduces type-check for the internal pointers.

Source/bindings/core/v8/NPV8Object.h

Index: Source/bindings/core/v8/NPV8Object.h
diff --git a/Source/bindings/core/v8/NPV8Object.h b/Source/bindings/core/v8/NPV8Object.h
index 5c99ca20350aa681e07b916dffd31846355fa8f9..9be5e8e08f00ce17836b12ab6ad28f722841d481 100644
--- a/Source/bindings/core/v8/NPV8Object.h
+++ b/Source/bindings/core/v8/NPV8Object.h
@@ -41,6 +41,7 @@
 namespace blink {
 
 class LocalDOMWindow;
+class ScriptWrappableBase;
 
 static const int npObjectInternalFieldCount = v8DefaultWrapperInternalFieldCount + 0;
 
@@ -73,6 +74,8 @@ bool isWrappedNPObject(v8::Handle<v8::Object>);
 
 V8NPObject* npObjectToV8NPObject(NPObject*);
 
+ScriptWrappableBase* npObjectToInternalPointer(NPObject*);
+
 void disposeUnderlyingV8Object(NPObject*, v8::Isolate*);
 
 } // namespace blink