Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/simple_inferrer_const_closure2_test.dart

Index: tests/compiler/dart2js/simple_inferrer_const_closure2_test.dart
diff --git a/tests/compiler/dart2js/simple_inferrer_const_closure2_test.dart b/tests/compiler/dart2js/simple_inferrer_const_closure2_test.dart
index c4c9194e91ffe18763191f0cb0c2dc3ff54566c4..458318b2f36fcf23c47e702611119b7dd7fd6321 100644
--- a/tests/compiler/dart2js/simple_inferrer_const_closure2_test.dart
+++ b/tests/compiler/dart2js/simple_inferrer_const_closure2_test.dart
@@ -33,10 +33,8 @@ void main() {
 
         checkReturn(String name, type) {
           var element = findElement(compiler, name);
-          Expect.equals(
-              type,
-              typesInferrer.getReturnTypeOfElement(element).simplify(compiler),
-              name);
+          dynamic returnType = typesInferrer.getReturnTypeOfElement(element);
+          Expect.equals(type, returnType.simplify(compiler), name);
         }
 
         checkReturn('method', closedWorld.commonMasks.numType);