Simplify class_hierarchy_test: remove abstract class

Change-Id: I805325a165a8d0540c3c839b656cc39fb898228a
Reviewed-on: https://dart-review.googlesource.com/c/92980
Reviewed-by: Jens Johansen <jensj@google.com>
diff --git a/pkg/kernel/test/class_hierarchy_test.dart b/pkg/kernel/test/class_hierarchy_test.dart
index 956c0cf..c49084b 100644
--- a/pkg/kernel/test/class_hierarchy_test.dart
+++ b/pkg/kernel/test/class_hierarchy_test.dart
@@ -18,7 +18,15 @@
 }
 
 @reflectiveTest
-class ClosedWorldClassHierarchyTest extends _ClassHierarchyTest {
+class ClosedWorldClassHierarchyTest {
+  Component component;
+  CoreTypes coreTypes;
+
+  /// The test library.
+  Library library;
+
+  ClassHierarchy _hierarchy;
+
   ClassHierarchy createClassHierarchy(Component component) {
     return new ClassHierarchy(component);
   }
@@ -208,16 +216,6 @@
     expect(cwchst.getSubtypesOf(g), unorderedEquals([g, h]));
     expect(cwchst.getSubtypesOf(h), unorderedEquals([h]));
   }
-}
-
-abstract class _ClassHierarchyTest {
-  Component component;
-  CoreTypes coreTypes;
-
-  /// The test library.
-  Library library;
-
-  ClassHierarchy _hierarchy;
 
   /// Return the new or existing instance of [ClassHierarchy].
   ClassHierarchy get hierarchy {
@@ -268,8 +266,6 @@
         implementedTypes: implements_.map((c) => c.asThisSupertype).toList()));
   }
 
-  ClassHierarchy createClassHierarchy(Component component);
-
   Procedure newEmptyGetter(String name,
       {DartType returnType: const DynamicType(), bool isAbstract: false}) {
     var body =