Enable the WebIDL [Exposed] annotation on an interface's members.

Source/bindings/tests/idls/TestExposedInterface.idl

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+[
+    Exposed=Worker&Window&ServiceWorker
+] interface TestExposedInterface {
+    void alwaysExposedMethod();
+    [Exposed=Worker] void workerExposedMethod();
+    [Exposed=Window] void windowExposedMethod();
+
+    static void alwaysExposedStaticMethod();
+    [Exposed=Worker] static void workerExposedStaticMethod();
+    [Exposed=Window] static void windowExposedStaticMethod();
+
+    attribute long alwaysExposedAttribute;
+    [Exposed=Worker] attribute long workerExposedAttribute;
+    [Exposed=Window] attribute long windowExposedAttribute;
+
+    [Exposed=Window&ServiceWorker] void windowAndServiceWorkerExposedMethod();
+};