Bug 822712 - SimplePush - Add PushManager to the test_interfaces.html test. r=dougt

dom/tests/mochitest/general/test_interfaces.html

@@ -546,7 +546,8 @@ var interfaceNamesInGlobalScope =
     "GamepadButtonEvent",
     "GamepadAxisMoveEvent",
     "SpeechRecognitionEvent",
-    "SpeechRecognitionError"
+    "SpeechRecognitionError",
+    "PushManager"
   ]
 
 for (var i in SpecialPowers.Components.interfaces) {