Fix gDevTools getter in the actor module (backend)

Author: janodvarko

lib/wsm-actor.js

@@ -13,13 +13,18 @@ const Events = require("sdk/event/core");
 
 // DevTools
 // See also: https://bugzilla.mozilla.org/show_bug.cgi?id=912121
+// We can't use the core/devtools.js module since this code is
+// executed on the backend.
 var devtools;
 try {
-  devtools = Cu.import("resource://gre/modules/devtools/shared/Loader.jsm", {}).devtools;
+  devtools = Cu.import("resource://devtools/shared/Loader.jsm", {}).devtools;
 } catch (err) {
-  devtools = Cu.import("resource://gre/modules/devtools/Loader.jsm", {}).devtools;
+  try {
+      devtools = Cu.import("resource://gre/modules/devtools/shared/Loader.jsm", {}).devtools;
+  } catch (err) {
+      devtools = Cu.import("resource://gre/modules/devtools/Loader.jsm", {}).devtools;
+  }
 }
-
 const { expectState } = devtools["require"]("devtools/server/actors/common");
 const protocol = devtools["require"]("devtools/server/protocol");