[bindings] Implement an ExperimentEnabled IDL extended attribute.

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

Index: third_party/WebKit/Source/bindings/templates/attributes.cpp
diff --git a/third_party/WebKit/Source/bindings/templates/attributes.cpp b/third_party/WebKit/Source/bindings/templates/attributes.cpp
index 89604a191368913c98024872a6205b5d2d9ea3b4..64b21da81ab04751f304240938485908eacf6caa 100644
--- a/third_party/WebKit/Source/bindings/templates/attributes.cpp
+++ b/third_party/WebKit/Source/bindings/templates/attributes.cpp
@@ -11,6 +11,15 @@ const v8::PropertyCallbackInfo<v8::Value>& info
 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 %}
@@ -207,6 +216,15 @@ const v8::FunctionCallbackInfo<v8::Value>& info
 {% 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}});
@@ -467,8 +485,7 @@ bool {{v8_class}}::PrivateScript::{{attribute.name}}AttributeSetter(LocalFrame*
 {% 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