Tidy finds WebIDLs with no spec.

Closes #6689

components/script/dom/webidls/TestBinding.webidl

@@ -2,6 +2,9 @@
  * 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/. */
 
+// This interface is entirely internal to Servo, and should not be accessible to
+// web pages.
+
 enum TestEnum { "", "foo", "bar" };
 
 dictionary TestDictionary {