Bug 1309961 - don't allow preferences to interfere with running updateManagerXML.js test. r=mhowell

toolkit/mozapps/update/tests/unit_aus_update/remoteUpdateXML.js

@@ -14,6 +14,11 @@ function run_test() {
   start_httpserver();
   setUpdateURLOverride(gURLData + gHTTPHandlerPath);
   setUpdateChannel("test_channel");
+
+  // This test expects that the app.update.download.backgroundInterval
+  // preference doesn't already exist.
+  Services.prefs.deleteBranch("app.update.download.backgroundInterval");
+
   standardInit();
   do_execute_soon(run_test_pt01);
 }

toolkit/mozapps/update/tests/unit_aus_update/updateManagerXML.js

@@ -12,6 +12,10 @@ function run_test() {
 
   setUpdateChannel("test_channel");
 
+  // This test expects that the app.update.download.backgroundInterval
+  // preference doesn't already exist.
+  Services.prefs.deleteBranch("app.update.download.backgroundInterval");
+
   // XXXrstrong - not specifying a detailsURL will cause a leak due to bug 470244
   // and until bug 470244 is fixed this will not test the value for detailsURL
   // when it isn't specified in the update xml.