Record ClassTypeAlias(s) as subtypes.

pkg/analyzer/test/src/dart/analysis/index_test.dart

Index: pkg/analyzer/test/src/dart/analysis/index_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/index_test.dart b/pkg/analyzer/test/src/dart/analysis/index_test.dart
index 1ab740d1d10bb84af570dbeac5619d8cf2e237a5..4c21bd138ed619e4e2a7c4282a188dbe2cbbffc3 100644
--- a/pkg/analyzer/test/src/dart/analysis/index_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/index_test.dart
@@ -916,7 +916,7 @@ class A {
       ..isWrittenAt('field = 5', true);
   }
 
-  test_subtypes() async {
+  test_subtypes_classDeclaration() async {
     String libP = 'package:test/lib.dart;package:test/lib.dart';
     provider.newFile(
         _p('$testProject/lib.dart'),
@@ -975,6 +975,38 @@ class Z implements E, D {
     }
   }
 
+  test_subtypes_classTypeAlias() async {
+    String libP = 'package:test/lib.dart;package:test/lib.dart';
+    provider.newFile(
+        _p('$testProject/lib.dart'),
+        '''
+class A {}
+class B {}
+class C {}
+class D {}
+''');
+    await _indexTestUnit('''
+import 'lib.dart';
+
+class X = A with B, C;
+class Y = A with B implements C, D;
+''');
+
+    {
+      AnalysisDriverSubtype X =
+          index.subtypes.singleWhere((t) => t.name == 'X');
+      expect(X.supertypes, ['$libP;A', '$libP;B', '$libP;C']);
+      expect(X.members, isEmpty);
+    }
+
+    {
+      AnalysisDriverSubtype Y =
+          index.subtypes.singleWhere((t) => t.name == 'Y');
+      expect(Y.supertypes, ['$libP;A', '$libP;B', '$libP;C', '$libP;D']);
+      expect(Y.members, isEmpty);
+    }
+  }
+
   test_subtypes_dynamic() async {
     await _indexTestUnit('''
 class X extends dynamic {