Issue 12343: Add pref-gated methods and test for activatable element states

components/script/dom/webidls/ActivatableElement.webidl

@@ -0,0 +1,15 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Interface for testing element activation
+// This interface is entirely internal to Servo, and should not be accessible to
+// web pages.
+[Exposed=(Window,Worker), NoInterfaceObject]
+interface ActivatableElement {
+  [Throws, Pref="dom.testing.element.activation.enabled"]
+  void enterFormalActivationState();
+
+  [Throws, Pref="dom.testing.element.activation.enabled"]
+  void exitFormalActivationState();
+};