Implement getDispatchTarget() in IncrementalClassHierarchy.

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 56b4eb64b27e2b4296b42f2fa7b1b7bc5c279293..14f527458d807ee29c876c7168cec19eedf69ae0 100644
--- a/pkg/kernel/test/class_hierarchy_test.dart
+++ b/pkg/kernel/test/class_hierarchy_test.dart
@@ -63,16 +63,6 @@ class IncrementalClassHierarchyTest extends _ClassHierarchyTest {
   }
 
   @failingTest
-  void test_getDispatchTarget() {
-    super.test_getDispatchTarget();
-  }
-
-  @failingTest
-  void test_getDispatchTarget_abstract() {
-    super.test_getDispatchTarget_abstract();
-  }
-
-  @failingTest
   void test_getInterfaceMember_extends() {
     super.test_getInterfaceMember_extends();
   }