Add LibraryElementForLink.isDartAsync.

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

Index: pkg/analyzer/test/src/summary/linker_test.dart
diff --git a/pkg/analyzer/test/src/summary/linker_test.dart b/pkg/analyzer/test/src/summary/linker_test.dart
index 530270af8e7d6632498c33df154a6252a5974519..28bcb565109ba4b8dba97edfaa053435c6e0869e 100644
--- a/pkg/analyzer/test/src/summary/linker_test.dart
+++ b/pkg/analyzer/test/src/summary/linker_test.dart
@@ -66,6 +66,21 @@ class C<V> extends B<V> {
     // 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 {