[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.experimental_api_name %}
+    String errorMessage;

[haraken, 2015/12/16 02:16:41]

What is this errorMessage for?

[Daniel Nishi, 2015/12/16 21:42:02]

It explains why an experiment may have failed.

When the error is unnecessary, I've changed the patch to not take a useless
error string.

+    if (!Experiments::isApiEnabled(currentExecutionContext(info.GetIsolate()), "{{ attribute.experimental_api_name }}", errorMessage)) {

[haraken, 2015/12/16 02:16:41]

Do you have a CL to implement the isAPIEnabled?

I'm fine with landing this CL without Experiments.h but want to see how it
looks.

[Daniel Nishi, 2015/12/16 21:42:02]

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+        v8SetReturnValue(info, v8::Undefined(info.GetIsolate()));
+        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 437 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' %}
+       'is%sExperimentallyEnabled' % attribute.name if attribute.experimental_api_name else 'v8ConstructorAttributeGetter' %}

[haraken, 2015/12/16 02:16:41]

Avoid using "if ... else ... if ... else".

[Daniel Nishi, 2015/12/16 21:42:02]

I've removed this by eliminating is%sExperimentallyEnabled.

 {% 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 %}