[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 66401dda85cde0d7254b0e051be5df5164f6ee48..441b774cd3443543628d193b461388a972153d0e 100644
--- a/third_party/WebKit/Source/bindings/templates/attributes.cpp
+++ b/third_party/WebKit/Source/bindings/templates/attributes.cpp
@@ -1,5 +1,4 @@
-{% from 'utilities.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value %}
-
+{% from 'utilities.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value, check_api_experiment %}
 
 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
@@ -11,6 +10,9 @@ const v8::PropertyCallbackInfo<v8::Value>& info
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- endif %})
 {
+    {% if attribute.is_api_experiment_enabled %}
+    {{check_api_experiment(attribute) | indent}}
+    {% 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 %}
@@ -178,6 +180,9 @@ const v8::FunctionCallbackInfo<v8::Value>& info
     {% if attribute.measure_as %}
     UseCounter::countIfNotPrivateScript(info.GetIsolate(), callingExecutionContext(info.GetIsolate()), UseCounter::{{attribute.measure_as('AttributeGetter')}});
     {% endif %}
+    {% if attribute.is_api_experiment_enabled %}
+    {{check_api_experiment(attribute) | indent}}
+    {% endif %}
     {% if world_suffix in attribute.activity_logging_world_list_for_getter %}
     ScriptState* scriptState = ScriptState::from(info.GetIsolate()->GetCurrentContext());
     V8PerContextData* contextData = scriptState->perContextData();
@@ -211,6 +216,9 @@ static void {{attribute.name}}ConstructorGetterCallback{{world_suffix}}(v8::Loca
     {% if attribute.measure_as %}
     UseCounter::countIfNotPrivateScript(info.GetIsolate(), callingExecutionContext(info.GetIsolate()), UseCounter::{{attribute.measure_as('ConstructorGetter')}});
     {% endif %}
+    {% if attribute.is_api_experiment_enabled %}
+    {{check_api_experiment(attribute) | indent}}
+    {% endif %}
     v8ConstructorAttributeGetter(property, info);
     TRACE_EVENT_SET_SAMPLING_STATE("v8", "V8Execution");
 }
@@ -418,6 +426,10 @@ bool {{v8_class}}::PrivateScript::{{attribute.name}}AttributeGetter(LocalFrame*
     if (holder.IsEmpty())
         return false;
 
+    {% if attribute.is_api_experiment_enabled %}
+    {{check_api_experiment(attribute, "scriptState->isolate()") | indent}}
+    {% endif %}
+
     ExceptionState exceptionState(ExceptionState::GetterContext, "{{attribute.name}}", "{{cpp_class}}", scriptState->context()->Global(), scriptState->isolate());
     v8::Local<v8::Value> v8Value = PrivateScriptRunner::runDOMAttributeGetter(scriptState, scriptStateInUserScript, "{{cpp_class}}", "{{attribute.name}}", holder);
     if (v8Value.IsEmpty())