LibJS: Add "Heap" and "Runtime" subdirectories

Let's try to keep LibJS tidy as it expands. :^)

Libraries/LibJS/Runtime/Object.h

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/String.h>
+#include <LibJS/Forward.h>
+#include <LibJS/Runtime/Cell.h>
+#include <LibJS/Runtime/PrimitiveString.h>
+#include <LibJS/Runtime/Value.h>
+
+namespace JS {
+
+class Object : public Cell {
+public:
+    Object();
+    virtual ~Object();
+
+    Value get(String property_name) const;
+    void put(String property_name, Value);
+
+    void put_native_function(String property_name, AK::Function<Value(Object*, Vector<Value>)>);
+    void put_native_property(String property_name, AK::Function<Value(Object*)> getter, AK::Function<void(Object*, Value)> setter);
+
+    virtual bool is_function() const { return false; }
+    virtual bool is_native_function() const { return false; }
+    virtual bool is_string_object() const { return false; }
+    virtual bool is_native_property() const { return false; }
+
+    virtual const char* class_name() const override { return "Object"; }
+    virtual void visit_children(Cell::Visitor&) override;
+
+    Object* prototype() { return m_prototype; }
+    const Object* prototype() const { return m_prototype; }
+    void set_prototype(Object* prototype) { m_prototype = prototype; }
+
+    bool has_own_property(const String& property_name) const;
+    enum class PreferredType {
+        Default,
+        String,
+        Number,
+    };
+
+    virtual Value value_of() const { return Value(const_cast<Object*>(this)); }
+    virtual Value to_primitive(PreferredType preferred_type = PreferredType::Default) const;
+    virtual Value to_string() const;
+
+private:
+    HashMap<String, Value> m_properties;
+    Object* m_prototype { nullptr };
+};
+
+}