Implement IncrementalClassHierarchy.getRankedSuperclasses().

pkg/kernel/test/class_hierarchy_test.dart

Index: pkg/kernel/test/class_hierarchy_test.dart
diff --git a/pkg/kernel/test/class_hierarchy_test.dart b/pkg/kernel/test/class_hierarchy_test.dart
index b4d459dcab19955a8f84d187897eb5228bfb344f..40f674c4c1a19b9c31f400ec1220c9c609ab5c19 100644
--- a/pkg/kernel/test/class_hierarchy_test.dart
+++ b/pkg/kernel/test/class_hierarchy_test.dart
@@ -113,11 +113,6 @@ class IncrementalClassHierarchyTest extends _ClassHierarchyTest {
   }
 
   @failingTest
-  void test_getRankedSuperclasses() {
-    super.test_getRankedSuperclasses();
-  }
-
-  @failingTest
   void test_getTypeAsInstanceOf_generic_extends() {
     super.test_getTypeAsInstanceOf_generic_extends();
   }