Split World usage into open, inference, and closed world.

tests/compiler/dart2js/subtypeset_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 subtypeset_test;
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
@@ skipping 27 matching lines @@
       main() {
         new A();
         new C();
         new D();
         new E();
         new F();
         new G();
       }
       """,
       useMockCompiler: false).then((env) {
-    World world = env.compiler.world;
+    World world = env.compiler.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 13 matching lines @@
     checkClass(B, [B, D, E]);
     checkClass(C, [C, E, F, G, H, B, D, I]);
     checkClass(D, [D]);
     checkClass(E, [E]);
     checkClass(F, [F]);
     checkClass(G, [G]);
     checkClass(H, [H, I]);
     checkClass(I, [I]);
   }));
 }