Further reduce use of Compiler.closedWorld.

tests/compiler/dart2js/class_set_test.dart

Index: tests/compiler/dart2js/class_set_test.dart
diff --git a/tests/compiler/dart2js/class_set_test.dart b/tests/compiler/dart2js/class_set_test.dart
index 9eea4f166340cd6f99fde142d9c318b85330665a..d5e66246b406528abbfbf679a2caaf6d89730215 100644
--- a/tests/compiler/dart2js/class_set_test.dart
+++ b/tests/compiler/dart2js/class_set_test.dart
@@ -50,7 +50,7 @@ testIterators() async {
       }
       """,
       useMockCompiler: false);
-  ClosedWorld world = env.compiler.closedWorld;
+  ClosedWorld world = env.closedWorld;
 
   ClassElement A = env.getElement("A");
   ClassElement B = env.getElement("B");
@@ -383,7 +383,7 @@ testForEach() async {
       }
       """,
       useMockCompiler: false);
-  ClosedWorld world = env.compiler.closedWorld;
+  ClosedWorld world = env.closedWorld;
 
   ClassElement A = env.getElement("A");
   ClassElement B = env.getElement("B");