Make sure to wrap all callbacks with expectAsync in tests

pkg/intl/test/find_default_locale_browser_test.dart

Index: pkg/intl/test/find_default_locale_browser_test.dart
===================================================================
--- pkg/intl/test/find_default_locale_browser_test.dart	(revision 13089)
+++ pkg/intl/test/find_default_locale_browser_test.dart	(working copy)
@@ -14,8 +14,8 @@
     // should find a way to force the system locale before the test is run
     // and then verify that it's actually the correct value.
     Intl.systemLocale = 'xx_YY';
-    findSystemLocale();
-    expect(Intl.systemLocale, isNot(equals("xx_YY")));
+    var callback = expectAsync1(verifyLocale);
+    findSystemLocale().then(callback);
   });
 }