Remove Compiler.openWorld

tests/compiler/dart2js/union_type_test.dart

Index: tests/compiler/dart2js/union_type_test.dart
diff --git a/tests/compiler/dart2js/union_type_test.dart b/tests/compiler/dart2js/union_type_test.dart
index 65e6da6e3140a466a54b860772bd7da139b27559..8294d478d6ddc5362b654f9db76df7b944f1d2b1 100644
--- a/tests/compiler/dart2js/union_type_test.dart
+++ b/tests/compiler/dart2js/union_type_test.dart
@@ -22,8 +22,8 @@ main() {
       }
       """,
         useMockCompiler: false);
-    ClosedWorld world =
-        env.compiler.openWorld.closeWorld(env.compiler.reporter);
+    env.compiler.closeResolution();
+    ClosedWorld world = env.compiler.closedWorld;
     FlatTypeMask mask1 = new FlatTypeMask.exact(env.getElement('A'));
     FlatTypeMask mask2 = new FlatTypeMask.exact(env.getElement('B'));
     UnionTypeMask union1 = mask1.nonNullable().union(mask2, world);