Further reduce use of Compiler.closedWorld.

tests/compiler/dart2js/closure_tracer_test.dart

Index: tests/compiler/dart2js/closure_tracer_test.dart
diff --git a/tests/compiler/dart2js/closure_tracer_test.dart b/tests/compiler/dart2js/closure_tracer_test.dart
index f76bea14062688dbb9c386d1f1e60f4e1afb9cf9..b585ea454c145f6c103399e75b6324e7809f223a 100644
--- a/tests/compiler/dart2js/closure_tracer_test.dart
+++ b/tests/compiler/dart2js/closure_tracer_test.dart
@@ -154,13 +154,14 @@ void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   asyncTest(() => compiler.run(uri).then((_) {
-        var commonMasks = compiler.closedWorld.commonMasks;
         var typesInferrer = compiler.globalInference.typesInferrerInternal;
+        var closedWorld = typesInferrer.closedWorld;
+        var commonMasks = closedWorld.commonMasks;
 
         checkType(String name, type) {
           var element = findElement(compiler, name);
           var mask = typesInferrer.getReturnTypeOfElement(element);
-          Expect.equals(type.nullable(), simplify(mask, compiler), name);
+          Expect.equals(type.nullable(), simplify(mask, closedWorld), name);
         }
 
         checkType('testFunctionStatement', commonMasks.uint31Type);