Fix a corner case of building summaries from ASTs.

pkg/analyzer/test/src/summary/summary_common.dart

Index: pkg/analyzer/test/src/summary/summary_common.dart
diff --git a/pkg/analyzer/test/src/summary/summary_common.dart b/pkg/analyzer/test/src/summary/summary_common.dart
index bd6b3cd922f178d596c655ddd096369ad082b7fe..a0eb33433eb31df08a4d67979066535230ddf428 100644
--- a/pkg/analyzer/test/src/summary/summary_common.dart
+++ b/pkg/analyzer/test/src/summary/summary_common.dart
@@ -4002,6 +4002,19 @@ class C<T> {
     checkConstCycle('C', hasCycle: false);
   }
 
+  test_constructorCycle_referenceToGenericParameter_asSupertype() {
+    // It's not valid Dart but we need to make sure it doesn't crash
+    // summary generation.
+    serializeLibraryText(
+        '''
+class C<T> extends T {
+  const C();
+}
+''',
+        allowErrors: true);
+    checkConstCycle('C', hasCycle: false);
+  }
+
   test_constructorCycle_referenceToStaticMethod_inOtherClass() {
     serializeLibraryText('''
 class C {