LibJS: Oops, "instanceof" was backwards!

Fix the "instanceof" operator to check if the constructor's prototype
property occurs anywhere in the prototype chain of the instance object.

This patch also adds Object.setPrototypeOf() to make it possible to
create a test for this bug.

Thanks to DexesTTP for pointing this out! :^)

1 files changed, 1 insertions, 0 deletions

diff --git a/Libraries/LibJS/Runtime/Object.h b/Libraries/LibJS/Runtime/Object.h
index 041ea089ba..aa2d887cbe 100644
--- a/Libraries/LibJS/Runtime/Object.h
+++ b/Libraries/LibJS/Runtime/Object.h
@@ -62,6 +62,7 @@ public:
     Object* prototype() { return m_prototype; }
     const Object* prototype() const { return m_prototype; }
     void set_prototype(Object* prototype) { m_prototype = prototype; }
+    bool has_prototype(const Object* prototype) const;
 
     bool has_own_property(const FlyString& property_name) const;
     enum class PreferredType {