Fix V8 bindings for named constructors to set prototype object correctly

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

 {% extends 'interface_base.cpp.tmpl' %}
 
 {% set has_prepare_prototype_and_interface_object =
     unscopables or has_conditional_attributes_on_prototype or
     methods | conditionally_exposed(is_partial) %}
 {% set prepare_prototype_and_interface_object_func =
     '%s::preparePrototypeAndInterfaceObject' % v8_class
     if has_prepare_prototype_and_interface_object
     else 'nullptr' %}
 
@@ skipping 533 matching lines @@
 v8::Local<v8::FunctionTemplate> {{v8_class}}Constructor::domTemplate(v8::Isolate* isolate, const DOMWrapperWorld& world) {
   static int domTemplateKey; // This address is used for a key to look up the dom template.
   V8PerIsolateData* data = V8PerIsolateData::from(isolate);
   v8::Local<v8::FunctionTemplate> result = data->findInterfaceTemplate(world, &domTemplateKey);
   if (!result.IsEmpty())
     return result;
 
   result = v8::FunctionTemplate::New(isolate, {{v8_class}}ConstructorCallback);
   v8::Local<v8::ObjectTemplate> instanceTemplate = result->InstanceTemplate();
   instanceTemplate->SetInternalFieldCount({{v8_class}}::internalFieldCount);
   result->SetClassName(v8AtomicString(isolate, "{{cpp_class}}"));

[Yuki, 2017/02/23 06:26:10]

You need to set the class name to "Image" instead of "HTMLImageElement", here.
"{{named_constructor.name}}" should be "Image", I think.

[sashab, 2017/02/24 03:06:13]

Done! :) This fixes the problem.

   result->Inherit({{v8_class}}::domTemplate(isolate, world));

[Yuki, 2017/02/23 06:26:10]

IIUC, now we don't need this line, because you set "prototype" property in
NamedConstructorAttributeGetter.  Could you remove this line if the removal
doesn't cause any problem?

[sashab, 2017/02/24 03:06:13]

When I remove this I get the runtime error:

[7903:7945:0224/140232.765122:2754782287949:FATAL:V8GCController.cpp(110)] Check
failed: V8Node::hasInstance(wrapper, m_isolate). 
#0 0x7f0e956e4517 base::debug::StackTrace::StackTrace()
#1 0x7f0e9570887b logging::LogMessage::~LogMessage()
#2 0x7f0e90dd3a2f
blink::MinorGCUnmodifiedWrapperVisitor::VisitPersistentHandle()
#3 0x7f0e92f16db2 v8::VisitorAdapter::VisitEmbedderReference()
#4 0x7f0e9333a5c3
v8::internal::GlobalHandles::IterateWeakRootsInNewSpaceWithClassIds()
#5 0x7f0e92f0d17c v8::Isolate::VisitWeakHandles()
#6 0x7f0e90dd0ac7 blink::V8GCController::gcPrologue()
#7 0x7f0e93349f38 v8::internal::Heap::CallGCPrologueCallbacks()
...

So I think it's still needed! :)

   data->setInterfaceTemplate(world, &domTemplateKey, result);
   return result;
 }
 
+void {{v8_class}}Constructor::NamedConstructorAttributeGetter(
+    v8::Local<v8::Name> propertyName,
+    const v8::PropertyCallbackInfo<v8::Value>& info) {
+  v8::Local<v8::Context> creationContext = info.Holder()->CreationContext();
+  V8PerContextData* perContextData = V8PerContextData::from(creationContext);
+  if (!perContextData) {
+    // TODO(yukishiino): Return a valid named constructor even after the context is detached
+    return;
+  }
+
+  v8::Local<v8::Function> namedConstructor = perContextData->constructorForType(&{{v8_class}}Constructor::wrapperTypeInfo);
+
+  // Set the prototype of named constructors to the regular constructor.
+  auto privateProperty = V8PrivateProperty::getNamedConstructorInitialized(info.GetIsolate());
+  v8::Local<v8::Context> currentContext = info.GetIsolate()->GetCurrentContext();
+  v8::Local<v8::Value> privateValue = privateProperty.get(currentContext, namedConstructor);
+
+  if (privateValue.IsEmpty()) {
+    v8::Local<v8::Function> interface = perContextData->constructorForType(&{{v8_class}}::wrapperTypeInfo);
+    v8::Local<v8::Value> interfacePrototype = interface->Get(currentContext, v8AtomicString(info.GetIsolate(), "prototype")).ToLocalChecked();
+    bool result = namedConstructor->Set(currentContext, v8AtomicString(info.GetIsolate(), "prototype"), interfacePrototype).ToChecked();
+    if (!result)
+      return;
+    privateProperty.set(currentContext, namedConstructor, v8::True(info.GetIsolate()));
+  }
+
+  v8SetReturnValue(info, namedConstructor);
+}
+
 {% endif %}
 {% endblock %}
 
 {##############################################################################}
 {% block overloaded_constructor %}
 {% if constructor_overloads %}
 static void constructor(const v8::FunctionCallbackInfo<v8::Value>& info) {
   ExceptionState exceptionState(info.GetIsolate(), ExceptionState::ConstructionContext, "{{interface_name}}");
   {# 2. Initialize argcount to be min(maxarg, n). #}
   switch (std::min({{constructor_overloads.maxarg}}, info.Length())) {
@@ skipping 322 matching lines @@
 }
 
 {% for method in methods if method.overloads and method.overloads.has_partial_overloads %}
 void {{v8_class}}::register{{method.name | blink_capitalize}}MethodForPartialInterface(void (*method)(const v8::FunctionCallbackInfo<v8::Value>&)) {
   {{cpp_class}}V8Internal::{{method.name}}MethodForPartialInterface = method;
 }
 
 {% endfor %}
 {% endif %}
 {% endblock %}