[bindings] Implement an ExperimentEnabled IDL extended attribute.

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

Index: third_party/WebKit/Source/bindings/templates/constants.cpp
diff --git a/third_party/WebKit/Source/bindings/templates/constants.cpp b/third_party/WebKit/Source/bindings/templates/constants.cpp
index bac23ca38f6fa129543b54c134c7c6d3b8336fa0..7e9ebe445613c607e4a864c2425a80a84ae27c24 100644
--- a/third_party/WebKit/Source/bindings/templates/constants.cpp
+++ b/third_party/WebKit/Source/bindings/templates/constants.cpp
@@ -34,13 +34,22 @@ const V8DOMConfiguration::ConstantConfiguration {{v8_class}}Constants[] = {
 };
 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 %}
@@ -48,6 +57,13 @@ V8DOMConfiguration::installConstant(isolate, functionTemplate, prototypeTemplate
 {% 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 %}