Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/simple_inferrer_const_closure_test.dart

Index: tests/compiler/dart2js/simple_inferrer_const_closure_test.dart
diff --git a/tests/compiler/dart2js/simple_inferrer_const_closure_test.dart b/tests/compiler/dart2js/simple_inferrer_const_closure_test.dart
index 6183de0c2aa08149065a428c84d509bcbc1d03c9..13e6876180351d217da9760fab02c809eadbebbe 100644
--- a/tests/compiler/dart2js/simple_inferrer_const_closure_test.dart
+++ b/tests/compiler/dart2js/simple_inferrer_const_closure_test.dart
@@ -42,10 +42,8 @@ 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('method1', closedWorld.commonMasks.uint31Type);