Stop using LibraryElement.visibleLibraries getter.

R=brianwilkerson@google.com, jmesserly@google.com
BUG=

Review URL: https://codereview.chromium.org//2336903002 .
diff --git a/test/codegen/recorder_test.dart b/test/codegen/recorder_test.dart
index b2d8019..912ca09 100644
--- a/test/codegen/recorder_test.dart
+++ b/test/codegen/recorder_test.dart
@@ -89,8 +89,7 @@
       recorder.lookupParent(lib.getType('F2'));
       recorder.lookupParent(lib.getType('G'));
       recorder.lookupParent(lib.getType('H'));
-      var coreLib =
-          lib.visibleLibraries.firstWhere((l) => l.displayName == 'dart.core');
+      var coreLib = lib.context.typeProvider.objectType.element.library;
       recorder.lookupParent(coreLib.getType('int'));
       recorder.lookupParent(coreLib.getType('num'));