src: add ClearWrap() to util.h

Counterpart to Wrap(), clears the previously assigned internal field.
Will be used in an upcoming commit.

Reviewed-by: Trevor Norris <trev.norris@gmail.com>

src/util-inl.h

@@ -107,6 +107,10 @@ void Wrap(v8::Local<v8::Object> object, TypeName* pointer) {
   object->SetAlignedPointerInInternalField(0, pointer);
 }
 
+void ClearWrap(v8::Local<v8::Object> object) {
+  Wrap<void>(object, NULL);
+}
+
 template <typename TypeName>
 TypeName* Unwrap(v8::Local<v8::Object> object) {
   assert(!object.IsEmpty());

src/util.h

@@ -112,6 +112,8 @@ inline v8::Local<v8::String> OneByteString(v8::Isolate* isolate,
 
 inline void Wrap(v8::Local<v8::Object> object, void* pointer);
 
+inline void ClearWrap(v8::Local<v8::Object> object);
+
 template <typename TypeName>
 inline TypeName* Unwrap(v8::Local<v8::Object> object);