Introduce isAbstractlyInstantiated to avoid exact masks of abstract classes.

tests/compiler/dart2js/jsinterop/world_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 jsinterop.world_test;
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/elements/elements.dart' show Element, ClassElement;
 import 'package:compiler/src/js_backend/js_backend.dart';
 import 'package:compiler/src/world.dart';
 import '../type_test_helper.dart';
 
 void main() {
   asyncTest(() async {
     await testClasses();
   });
 }
 
 testClasses() async {
   test(String mainSource,
       {List<String> directlyInstantiated: const <String>[],
+      List<String> abstractlyInstantiated: const <String>[],
       List<String> indirectlyInstantiated: const <String>[]}) async {
     TypeEnvironment env = await TypeEnvironment.create(
         r"""
 @JS()
 class A {
   get foo;
 
   external A(var foo);
 }
 
@@ skipping 79 matching lines @@
     for (String name in classEnvironment.keys) {
       ClassElement cls = classEnvironment[name];
       bool isInstantiated = false;
       if (directlyInstantiated.contains(name)) {
         isInstantiated = true;
         Expect.isTrue(
             world.isDirectlyInstantiated(cls),
             "Expected $name to be directly instantiated in `${mainSource}`:"
             "\n${world.dump(cls)}");
       }
+      if (abstractlyInstantiated.contains(name)) {
+        isInstantiated = true;
+        Expect.isTrue(
+            world.isAbstractlyInstantiated(cls),
+            "Expected $name to be abstractly instantiated in `${mainSource}`:"
+            "\n${world.dump(cls)}");
+      }
       if (indirectlyInstantiated.contains(name)) {
         isInstantiated = true;
         Expect.isTrue(
             world.isIndirectlyInstantiated(cls),
             "Expected $name to be indirectly instantiated in `${mainSource}`:"
             "\n${world.dump(cls)}");
       }
       if (!isInstantiated && (name != 'Object' && name != 'Interceptor')) {
         Expect.isFalse(
             world.isInstantiated(cls),
             "Expected $name to be uninstantiated in `${mainSource}`:"
             "\n${world.dump(cls)}");
       }
     }
   }
 
   await test('main() {}');
 
   await test('main() => newA();',
-      directlyInstantiated: ['A', 'B', 'C', 'D'],
+      abstractlyInstantiated: ['A', 'B', 'C', 'D'],
       indirectlyInstantiated: ['Object', 'Interceptor', 'JavaScriptObject']);
 
   await test('main() => newB();',
-      directlyInstantiated: ['A', 'B', 'C', 'D'],
+      abstractlyInstantiated: ['A', 'B', 'C', 'D'],
       indirectlyInstantiated: ['Object', 'Interceptor', 'JavaScriptObject']);
 
   await test('main() => newC();',
-      directlyInstantiated: ['A', 'B', 'C', 'D'],
+      abstractlyInstantiated: ['A', 'B', 'C', 'D'],
       indirectlyInstantiated: ['Object', 'Interceptor', 'JavaScriptObject']);
 
   await test('main() => newD();',
-      directlyInstantiated: ['A', 'B', 'C', 'D'],
+      abstractlyInstantiated: ['A', 'B', 'C', 'D'],
       indirectlyInstantiated: ['Object', 'Interceptor', 'JavaScriptObject']);
 
   await test('main() => newE();', directlyInstantiated: ['E']);
 
   await test('main() => newF();', directlyInstantiated: ['F']);
 
   await test('main() => [newD(), newE()];',
-      directlyInstantiated: ['A', 'B', 'C', 'D', 'E'],
+      directlyInstantiated: ['E'],
+      abstractlyInstantiated: ['A', 'B', 'C', 'D'],
       indirectlyInstantiated: ['Object', 'Interceptor', 'JavaScriptObject']);
 }