Bug 1132337 - fix "ReferenceError: PlacesTestUtils is not defined" in test_history_expiration.js. r=paolo

comm-central: TEST-UNEXPECTED-FAIL | toolkit/components/downloads/test/unit/test_history_expiration.js | xpcshell return code: 0

toolkit/components/downloads/test/unit/head_download_manager.js

@@ -17,6 +17,8 @@ Cu.import("resource://testing-common/httpd.js");
 Cu.import("resource://gre/modules/PlacesUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Promise",
                                   "resource://gre/modules/Promise.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesTestUtils",
+                                  "resource://testing-common/PlacesTestUtils.jsm");
 
 var downloadUtils = { };
 XPCOMUtils.defineLazyServiceGetter(downloadUtils,