Fix: FunctionTemplate::SetPrototypeAttributes broke prototype object

src/apinatives.js

Index: src/apinatives.js
diff --git a/src/apinatives.js b/src/apinatives.js
index 193863f5c2f9f99cccb42432b0b6902b47898aff..8c567b8f85407c6ba3fab3f3127c181ba00c8ce0 100644
--- a/src/apinatives.js
+++ b/src/apinatives.js
@@ -73,14 +73,10 @@ function InstantiateFunction(data, name) {
       if (name) %FunctionSetName(fun, name);
       cache[serialNumber] = fun;
       var prototype = %GetTemplateField(data, kApiPrototypeTemplateOffset);
-      var attributes = %GetTemplateField(data, kApiPrototypeAttributesOffset);
-      if (attributes != NONE) {
-        %IgnoreAttributesAndSetProperty(
-            fun, "prototype",
-            prototype ? Instantiate(prototype) : {},
-            attributes);
-      } else {
-        fun.prototype = prototype ? Instantiate(prototype) : {};
+      var flags = %GetTemplateField(data, kApiFlagOffset);
+      fun.prototype = prototype ? Instantiate(prototype) : {};
+      if (flags & (1 << kReadOnlyPrototypeBit)) {
+        %FunctionReadOnlyPrototype(fun);
       }
       %SetProperty(fun.prototype, "constructor", fun, DONT_ENUM);
       var parent = %GetTemplateField(data, kApiParentTemplateOffset);