Add LibraryElementForLink.isDartAsync.

pkg/analyzer/test/src/summary/linker_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.
 
 import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/link.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
 import 'summarize_ast_test.dart';
@@ skipping 48 matching lines @@
 }
 class C<V> extends B<V> {
   var j;
 }
 ''');
     LibraryElementForLink library = linker.getLibrary(linkerInputs.testDartUri);
     library.libraryCycleForLink.ensureLinked();
     // No assertions--just make sure it doesn't crash.
   }
 
+  void test_baseClass_genericWithGenericMethod_returnsGenericFuture() {
+    createLinker('''
+import 'dart:async';
+class B<T> {
+  Future<T> f() => null;
+}
+class C<T> extends B<T> {
+  Future<T> f() => null;
+}
+''');
+    LibraryElementForLink library = linker.getLibrary(linkerInputs.testDartUri);
+    library.libraryCycleForLink.ensureLinked();
+    // No assertions--just make sure it doesn't crash.
+  }
+
   void test_baseClass_withPrivateField() {
     createLinker('''
 class B {
   var _b;
 }
 class C extends B {
   var c;
 }
 ''');
     LibraryElementForLink library = linker.getLibrary(linkerInputs.testDartUri);
@@ skipping 372 matching lines @@
 class C extends B with I {}
 class D extends C {
   void f() {}
 }
 ''');
     LibraryElementForLink library = linker.getLibrary(linkerInputs.testDartUri);
     library.libraryCycleForLink.ensureLinked();
     // No assertions--just make sure it doesn't crash.
   }
 }