IDL compiler: move EventHandler null check out of generated bindings

Source/bindings/templates/attributes.cpp

 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 {% filter conditional(attribute.conditional_string) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(v8::Local<v8::String> name, const v8::PropertyCallbackInfo<v8::Value>& info)
 {
     {% if attribute.is_unforgeable %}
     v8::Handle<v8::Object> holder = info.This()->FindInstanceInPrototypeChain({{v8_class_name}}::GetTemplate(info.GetIsolate(), worldType(info.GetIsolate())));
     if (holder.IsEmpty())
         return;
     {{cpp_class_name}}* imp = {{v8_class_name}}::toNative(holder);
@@ skipping 107 matching lines @@
     {% if not attribute.is_static %}
     {{cpp_class_name}}* imp = {{v8_class_name}}::toNative(info.Holder());
     {% endif %}
     {% if attribute.idl_type == 'EventHandler' and interface_name == 'Window' %}
     if (!imp->document())
         return;
     {% endif %}
     {% if attribute.idl_type != 'EventHandler' %}
     {{attribute.v8_value_to_local_cpp_value}};
     {% else %}{# EventHandler hack #}
-    {# Non-callable input should be treated as null #}
-    if (!jsValue->IsNull() && !jsValue->IsFunction())
-        jsValue = v8::Null(info.GetIsolate());
     transferHiddenDependency(info.Holder(), {{attribute.event_handler_getter_expression}}, jsValue, {{v8_class_name}}::eventListenerCacheIndex, info.GetIsolate());
     {% endif %}
     {% if attribute.enum_validation_expression %}
     {# Setter ignores invalid enum values #}
     String string = cppValue;
     if (!({{attribute.enum_validation_expression}}))
         return;
     {% endif %}
     {% if attribute.is_reflect %}
     CustomElementCallbackDispatcher::CallbackDeliveryScope deliveryScope;
@@ skipping 40 matching lines @@
     {% endif %}
     {% if attribute.has_custom_setter %}
     {{v8_class_name}}::{{attribute.name}}AttributeSetterCustom(name, jsValue, info);
     {% else %}
     {{cpp_class_name}}V8Internal::{{attribute.name}}AttributeSetter{{world_suffix}}(name, jsValue, info);
     {% endif %}
     TRACE_EVENT_SET_SAMPLING_STATE("V8", "Execution");
 }
 {% endfilter %}
 {% endmacro %}