Avoid a crash during summary linking when there are inheritance errors.

pkg/analyzer/test/src/summary/resynthesize_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 test.src.serialization.elements_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 3607 matching lines @@
   }
 
   void test_inferredType_usesSyntheticFunctionType_functionTypedParam() {
     checkLibrary('''
 int f(int x(String y)) => null;
 String g(int x(String y)) => null;
 var v = [f, g];
 ''');
   }
 
+  test_inheritance_errors() {
+    checkLibrary('''
+abstract class A {
+  int m();
+}
+
+abstract class B {
+  String m();
+}
+
+abstract class C implements A, B {}
+
+abstract class D extends C {
+  var f;
+}
+''');
+  }
+
   test_initializer_executable_with_return_type_from_closure() {
     checkLibrary('var v = () => 0;');
   }
 
   test_initializer_executable_with_return_type_from_closure_field() {
     checkLibrary('''
 class C {
   var v = () => 0;
 }
 ''');
@@ skipping 1121 matching lines @@
       fail('Unexpectedly tried to get unlinked summary for $uri');
     }
     return serializedUnit;
   }
 
   @override
   bool hasLibrarySummary(String uri) {
     return true;
   }
 }