[bindings] Implement an ExperimentEnabled IDL extended attribute.

third_party/WebKit/Source/bindings/templates/attributes.cpp

 {% from 'conversions.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value %}
 
 
 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 {% filter conditional(attribute.conditional_string) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(
 {%- if attribute.is_data_type_property %}
 const v8::PropertyCallbackInfo<v8::Value>& info
 {%- else %}
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- endif %})
 {
+    {% if attribute.api_experiment_name %}
+    String errorMessage;
+    if (!Experiments::isApiEnabled(currentExecutionContext(info.GetIsolate()), "{{ attribute.api_experiment_name }}", errorMessage)) {
+        v8SetReturnValue(info, v8::Undefined(info.GetIsolate()));
+        Document& document = *toDocument(currentExecutionContext(info.GetIsolate()));
+        document.addConsoleMessage(ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, errorMessage));
+        return;
+    }
+    {% endif %}
     {% if attribute.is_reflect and not attribute.is_url
           and attribute.idl_type == 'DOMString' and is_node
           and not attribute.is_implemented_in_private_script %}
     {% set cpp_class, v8_class = 'Element', 'V8Element' %}
     {% endif %}
     {# holder #}
     {% if not attribute.is_static %}
     {% if attribute.is_lenient_this %}
     v8::Local<v8::Object> holder = {{v8_class}}::findInstanceInPrototypeChain(info.This(), info.GetIsolate());
     if (holder.IsEmpty())
@@ skipping 176 matching lines @@
 }
 {% endfilter %}
 {% endmacro %}
 
 
 {##############################################################################}
 {% macro constructor_getter_callback(attribute, world_suffix) %}
 {% filter conditional(attribute.conditional_string) %}
 static void {{attribute.name}}ConstructorGetterCallback{{world_suffix}}(v8::Local<v8::Name> property, const v8::PropertyCallbackInfo<v8::Value>& info)
 {
+    {% if attribute.api_experiment_name %}

[Daniel Nishi, 2015/12/16 21:42:03]

I've replaced the is%sExperimentallyEnabled with this. This implements the
return undefined and give a friendly message about why it failed concept.

+    String errorMessage;
+    if (!Experiments::isApiEnabled(currentExecutionContext(info.GetIsolate()), "{{ attribute.api_experiment_name }}", errorMessage)) {
+        v8SetReturnValue(info, v8::Undefined(info.GetIsolate()));
+        Document& document = *toDocument(currentExecutionContext(info.GetIsolate()));
+        document.addConsoleMessage(ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, errorMessage));
+        return;
+    }
+    {% endif %}
     TRACE_EVENT_SET_SAMPLING_STATE("blink", "DOMGetter");
     {% if attribute.deprecate_as %}
     UseCounter::countDeprecationIfNotPrivateScript(info.GetIsolate(), callingExecutionContext(info.GetIsolate()), UseCounter::{{attribute.deprecate_as}});
     {% endif %}
     {% if attribute.measure_as %}
     UseCounter::countIfNotPrivateScript(info.GetIsolate(), callingExecutionContext(info.GetIsolate()), UseCounter::{{attribute.measure_as('ConstructorGetter')}});
     {% endif %}
     v8ConstructorAttributeGetter(property, info);
     TRACE_EVENT_SET_SAMPLING_STATE("v8", "V8Execution");
 }
@@ skipping 240 matching lines @@
 }
 {% endmacro %}
 
 
 {##############################################################################}
 {% macro attribute_configuration(attribute) %}
 {% from 'conversions.cpp' import property_location %}
 {% if attribute.constructor_type %}
 {% set getter_callback =
        '%sV8Internal::%sConstructorGetterCallback' % (cpp_class_or_partial, attribute.name)
-       if attribute.needs_constructor_getter_callback else
-       'v8ConstructorAttributeGetter' %}
+       if attribute.needs_constructor_getter_callback else 'v8ConstructorAttributeGetter' %}
 {% set setter_callback =
        '%sV8Internal::%sAttributeSetterCallback' % (cpp_class_or_partial, attribute.name)
        if attribute.needs_constructor_setter_callback else
        '%sV8Internal::%sConstructorAttributeSetterCallback' % (cpp_class_or_partial, cpp_class) %}
 {% else %}{# regular attributes #}
 {% set getter_callback = '%sV8Internal::%sAttributeGetterCallback' %
            (cpp_class_or_partial, attribute.name) %}
 {% set setter_callback = '%sV8Internal::%sAttributeSetterCallback' %
            (cpp_class_or_partial, attribute.name)
        if attribute.has_setter else '0' %}
@@ skipping 30 matching lines @@
        setter_callback_for_main_world,
        wrapper_type_info,
        access_control,
        property_attribute,
        only_exposed_to_private_script,
        property_location(attribute),
        holder_check,
    ] %}
 {{'{'}}{{attribute_configuration_list | join(', ')}}{{'}'}}
 {%- endmacro %}