Further reduce use of Compiler.closedWorld.

tests/compiler/dart2js/class_set_test.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.
 
 // Test for iterators on for [SubclassNode].
 
 library class_set_test;
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
@@ skipping 32 matching lines @@
       main() {
         new A();
         new C();
         new D();
         new E();
         new F();
         new G();
       }
       """,
       useMockCompiler: false);
-  ClosedWorld world = env.compiler.closedWorld;
+  ClosedWorld world = env.closedWorld;
 
   ClassElement A = env.getElement("A");
   ClassElement B = env.getElement("B");
   ClassElement C = env.getElement("C");
   ClassElement D = env.getElement("D");
   ClassElement E = env.getElement("E");
   ClassElement F = env.getElement("F");
   ClassElement G = env.getElement("G");
 
   void checkClass(ClassElement cls,
@@ skipping 312 matching lines @@
         new C();
         new D();
         new E();
         new F();
         new G();
         new H();
         new I();
       }
       """,
       useMockCompiler: false);
-  ClosedWorld world = env.compiler.closedWorld;
+  ClosedWorld world = env.closedWorld;
 
   ClassElement A = env.getElement("A");
   ClassElement B = env.getElement("B");
   ClassElement C = env.getElement("C");
   ClassElement D = env.getElement("D");
   ClassElement E = env.getElement("E");
   ClassElement F = env.getElement("F");
   ClassElement G = env.getElement("G");
   ClassElement H = env.getElement("H");
   ClassElement I = env.getElement("I");
@@ skipping 179 matching lines @@
   checkAny(B, [B, D], find: D, anySubtype: true, expectedResult: true);
   checkAny(B, [B, D, F, I], find: I, anySubtype: true, expectedResult: true);
 
   checkAny(X, [X, A, B, D, C, G, F, I, H, E],
       anySubtype: true, expectedResult: false);
   checkAny(X, [X, A], find: A, anySubtype: true, expectedResult: true);
   checkAny(X, [X, A, B, D], find: D, anySubtype: true, expectedResult: true);
   checkAny(X, [X, A, B, D, C, G, F, I],
       find: I, anySubtype: true, expectedResult: true);
 }