Bug 924929 - Add missing Cu import in session restore content code (r=Yoric)

browser/components/sessionstore/content/content-sessionStore.js

@@ -8,6 +8,8 @@ function debug(msg) {
   Services.console.logStringMessage("SessionStoreContent: " + msg);
 }
 
+let Cu = Components.utils;
+
 Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
 
 XPCOMUtils.defineLazyModuleGetter(this, "DocShellCapabilities",