Freeze global prototype chain per WebIDL

third_party/WebKit/Source/bindings/templates/interface.cpp.tmpl

Index: third_party/WebKit/Source/bindings/templates/interface.cpp.tmpl
diff --git a/third_party/WebKit/Source/bindings/templates/interface.cpp.tmpl b/third_party/WebKit/Source/bindings/templates/interface.cpp.tmpl
index 2686f5204e9fae0d8b2e80ceaaaa3c49bcd99f00..ad62a32111ef726d016bb97bf6c5e02a255c77d3 100644
--- a/third_party/WebKit/Source/bindings/templates/interface.cpp.tmpl
+++ b/third_party/WebKit/Source/bindings/templates/interface.cpp.tmpl
@@ -769,6 +769,8 @@ v8::Local<v8::FunctionTemplate> {{v8_class}}::domTemplateForNamedPropertiesObjec
 
   v8::Local<v8::ObjectTemplate> namedPropertiesObjectTemplate = namedPropertiesObjectFunctionTemplate->PrototypeTemplate();
   namedPropertiesObjectTemplate->SetInternalFieldCount({{v8_class}}::internalFieldCount);
+  // Named Properties object has SetPrototype method of Immutable Prototype Exotic Objects
+  namedPropertiesObjectTemplate->SetImmutableProto();
   V8DOMConfiguration::setClassString(isolate, namedPropertiesObjectTemplate, "{{interface_name}}Properties");
   {{install_named_property_handler('namedPropertiesObjectTemplate') | indent(2)}}