[bindings] Implement an ExperimentEnabled IDL extended attribute.

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

 {##############################################################################}
 {% macro constant_getter_callback(constant) %}
 {% filter conditional(constant.conditional_string) %}
 static void {{constant.name}}ConstantGetterCallback(v8::Local<v8::Name>, const v8::PropertyCallbackInfo<v8::Value>& info)
 {
     TRACE_EVENT_SET_SAMPLING_STATE("blink", "DOMGetter");
     {% if constant.deprecate_as %}
     UseCounter::countDeprecationIfNotPrivateScript(info.GetIsolate(), callingExecutionContext(info.GetIsolate()), UseCounter::{{constant.deprecate_as}});
     {% endif %}
     {% if constant.measure_as %}
@@ skipping 16 matching lines @@
 {% macro install_constants() %}
 {% if constant_configuration_constants %}
 {# Normal constants #}
 const V8DOMConfiguration::ConstantConfiguration {{v8_class}}Constants[] = {
     {% for constant in constant_configuration_constants %}
     {{constant_configuration(constant)}},
     {% endfor %}
 };
 V8DOMConfiguration::installConstants(isolate, functionTemplate, prototypeTemplate, {{v8_class}}Constants, WTF_ARRAY_LENGTH({{v8_class}}Constants));
 {% endif %}
+ExecutionContext* ec = currentExecutionContext(isolate);
+ALLOW_UNUSED_LOCAL(ec);
 {# Runtime-enabled constants #}
 {% for constant_tuple in runtime_enabled_constants %}
 {% filter runtime_enabled(constant_tuple[0]) %}
 {% for constant in constant_tuple[1] %}
 {% set constant_name = constant.name.title().replace('_', '') %}
+{% if constant.name in experimental_enabled_constants %}
+if (Experiments::isApiEnabledWithoutMessage(ec, "{{experimental_enabled_constants.get(constant.name)}}")) {
+    const V8DOMConfiguration::ConstantConfiguration constant{{constant_name}}Configuration = {{constant_configuration(constant)}};
+    V8DOMConfiguration::installConstant(isolate, functionTemplate, prototypeTemplate, constant{{constant_name}}Configuration);
+}
+{% else %}
 const V8DOMConfiguration::ConstantConfiguration constant{{constant_name}}Configuration = {{constant_configuration(constant)}};
 V8DOMConfiguration::installConstant(isolate, functionTemplate, prototypeTemplate, constant{{constant_name}}Configuration);
+{% endif %}
 {% endfor %}
 {% endfilter %}
 {% endfor %}
 {# Constants with [DeprecateAs] or [MeasureAs] #}
 {% for constant in special_getter_constants %}
 V8DOMConfiguration::installConstantWithGetter(isolate, functionTemplate, prototypeTemplate, "{{constant.name}}", {{cpp_class}}V8Internal::{{constant.name}}ConstantGetterCallback);
 {% endfor %}
+{# Constants with [ExperimentEnabled] only #}
+{% for constant in experimental_only_constants %}
+if (Experiments::isApiEnabledWithoutMessage(ec, "{{constant['api_experiment_name']}}")) {
+    const V8DOMConfiguration::ConstantConfiguration constant{{constant.name}}Configuration = {{constant_configuration(constant)}};
+    V8DOMConfiguration::installConstant(isolate, functionTemplate, prototypeTemplate, constant{{constant.name}}Configuration);
+}
+{% endfor %}
 {# Check constants #}
 {% if not do_not_check_constants %}
 {% for constant in constants %}
 {% if constant.idl_type not in ('Double', 'Float', 'String') %}
 {% set constant_cpp_class = constant.cpp_class or cpp_class %}
 static_assert({{constant.value}} == {{constant_cpp_class}}::{{constant.reflected_name}}, "the value of {{cpp_class}}_{{constant.reflected_name}} does not match with implementation");
 {% endif %}
 {% endfor %}
 {% endif %}
 {% endmacro %}
 
 
 {######################################}
 {%- macro constant_configuration(constant) %}
 {% if constant.idl_type in ('Double', 'Float') %}
     {% set value = '0, %s' % constant.value %}
 {% else %}
     {# 'Short', 'Long' etc. #}
     {% set value = '%s, 0' % constant.value %}
 {% endif %}
 {"{{constant.name}}", {{value}}, V8DOMConfiguration::ConstantType{{constant.idl_type}}}
 {%- endmacro %}