Checking heap objects in API.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 7b954983af19a451f4a6d26710e81dca89c3d246..1e018cb832d068fe98933c868d960fabe1dd52ea 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -437,6 +437,7 @@ class V8EXPORT HandleScope {
    * Creates a new handle with the given value.
    */
   static internal::Object** CreateHandle(internal::Object* value);
+  static internal::Object** CreateHandleFromHeapObject(internal::Object* value);
 
  private:
   // Make it impossible to create heap-allocated or illegal handle
@@ -3483,6 +3484,9 @@ class Internals {
     uint8_t* addr = reinterpret_cast<uint8_t*>(ptr) + offset - kHeapObjectTag;
     return *reinterpret_cast<T*>(addr);
   }
+
+  static inline bool IsHeapObject(void*) { return false; }
+  static inline bool IsHeapObject(Date*) { return true; }
 };
 
 }  // namespace internal
@@ -3499,7 +3503,12 @@ Local<T>::Local() : Handle<T>() { }
 template <class T>
 Local<T> Local<T>::New(Handle<T> that) {
   if (that.IsEmpty()) return Local<T>();
-  internal::Object** p = reinterpret_cast<internal::Object**>(*that);
+  T* that_ptr = *that;
+  internal::Object** p = reinterpret_cast<internal::Object**>(that_ptr);
+  if (internal::Internals::IsHeapObject(that_ptr)) {
+    return Local<T>(
+        reinterpret_cast<T*>(HandleScope::CreateHandleFromHeapObject(*p)));
+  }
   return Local<T>(reinterpret_cast<T*>(HandleScope::CreateHandle(*p)));
 }