Bug 951609 - Fix scope issues in child.js. r=ochameau

toolkit/devtools/server/child.js

@@ -1,6 +1,5 @@
-Cu.import("resource://gre/modules/Services.jsm");
-Cu.import("resource://gre/modules/devtools/dbg-server.jsm");
-Cu.import("resource://gre/modules/devtools/DevToolsUtils.jsm");
+const {DevToolsUtils} = Cu.import("resource://gre/modules/devtools/DevToolsUtils.jsm", {});
+const {DebuggerServer, ActorPool} = Cu.import("resource://gre/modules/devtools/dbg-server.jsm", {});
 
 if (!DebuggerServer.initialized) {
   DebuggerServer.init();