[Reland] Implement Custom Element's class side inheritance

Source/bindings/core/v8/CustomElementConstructorBuilder.cpp

Index: Source/bindings/core/v8/CustomElementConstructorBuilder.cpp
diff --git a/Source/bindings/core/v8/CustomElementConstructorBuilder.cpp b/Source/bindings/core/v8/CustomElementConstructorBuilder.cpp
index 5c57589d4347430d49734e7ef2356cb345bae8ad..07d975284ae9837da236ef45e51f24ab02051288 100644
--- a/Source/bindings/core/v8/CustomElementConstructorBuilder.cpp
+++ b/Source/bindings/core/v8/CustomElementConstructorBuilder.cpp
@@ -199,6 +199,14 @@ bool CustomElementConstructorBuilder::createConstructor(Document* document, Cust
     if (!v8CallBoolean(m_constructor->ForceSet(context, prototypeKey, m_prototype, v8::PropertyAttribute(v8::ReadOnly | v8::DontEnum | v8::DontDelete))))
         return false;
 
+    v8::Local<v8::String> constructorKey = v8String(isolate, "constructor");
+    v8::Local<v8::Value> constructorPrototype;
+    if (!m_prototype->Get(context, constructorKey).ToLocal(&constructorPrototype))
+        return false;
+
+    if (!v8CallBoolean(m_constructor->SetPrototype(context, constructorPrototype)))
+        return false;
+
     V8HiddenValue::setHiddenValue(isolate, m_prototype, V8HiddenValue::customElementIsInterfacePrototypeObject(isolate), v8::True(isolate));
     if (!v8CallBoolean(m_prototype->ForceSet(context, v8String(isolate, "constructor"), m_constructor, v8::DontEnum)))
         return false;