[DO NOT LAND] Set @@toStringTag for DOM object prototypes

Source/bindings/templates/interface_base.cpp

Index: Source/bindings/templates/interface_base.cpp
diff --git a/Source/bindings/templates/interface_base.cpp b/Source/bindings/templates/interface_base.cpp
index 1d817dd1f9eff827971e41c2c8afd5c37141524a..be331daabaada9df03d29876b6d4ddf260d6011f 100644
--- a/Source/bindings/templates/interface_base.cpp
+++ b/Source/bindings/templates/interface_base.cpp
@@ -469,6 +469,13 @@ static void install{{v8_class}}Template(v8::Local<v8::FunctionTemplate> function
     functionTemplate->SetHiddenPrototype(true);
     {% endif %}
 
+    {# Willful violation of WebIDL 4.5.4 and 4.7 - implement the class string
+       for interfaces via @@toStringTag on the prototype. WebIDL requires
+       @@toStringTag instances and prototype (with 'Prototype' appended) but
+       this has performance concerns and may not be necessary for web compat.
+       https://www.w3.org/Bugs/Public/show_bug.cgi?id=28244 #}
+    prototypeTemplate->Set(v8::Symbol::GetToStringTag(isolate), v8AtomicString(isolate, "{{interface_name}}"));
+
     // Custom toString template
     functionTemplate->Set(v8AtomicString(isolate, "toString"), V8PerIsolateData::from(isolate)->toStringTemplate());
     {% endif %}