Fix a corner case of building summaries from ASTs.

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

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.src.summary.summary_common;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
@@ skipping 3984 matching lines @@
         '''
 class C<T> {
   final x;
   const C() : x = T;
 }
 ''',
         allowErrors: true);
     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 {
   final x;
   const C() : x = D.f;
 }
 class D {
   static void f() {}
 }
 ''');
@@ skipping 4051 matching lines @@
 class _PrefixExpectation {
   final ReferenceKind kind;
   final String name;
   final String absoluteUri;
   final String relativeUri;
   final int numTypeParameters;
 
   _PrefixExpectation(this.kind, this.name,
       {this.absoluteUri, this.relativeUri, this.numTypeParameters: 0});
 }