Fix for a new infinite cycle in InterfaceTypeImpl.substitute2().

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

 // Copyright (c) 2016, 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.driver;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1313 matching lines @@
 
   test_getResult_notDartFile() async {
     var path = _p('/test/lib/test.txt');
     provider.newFile(path, 'class A {}');
 
     AnalysisResult result = await driver.getResult(path);
     expect(result, isNotNull);
     expect(result.unit.element.types.map((e) => e.name), ['A']);
   }
 
+  test_getResult_recursiveFlatten() async {
+    String content = r'''
+import 'dart:async';
+class C<T> implements Future<C<T>> {}
+''';
+    addTestFile(content);
+    // Should not throw exceptions.
+    await driver.getResult(testFile);
+  }
+
   test_getResult_sameFile_twoUris() async {
     var a = _p('/test/lib/a.dart');
     var b = _p('/test/lib/b.dart');
     var c = _p('/test/test/c.dart');
     provider.newFile(a, 'class A<T> {}');
     provider.newFile(
         b,
         r'''
 import 'a.dart';
 var VB = new A<int>();
@@ skipping 1031 matching lines @@
    * Return the [provider] specific path for the given Posix [path].
    */
   String _p(String path) => provider.convertPath(path);
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }
 
 class _SourceMock extends TypedMock implements Source {}