Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/issue13354_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 import 'type_mask_test_helper.dart';
 
 const String TEST = """
@@ skipping 25 matching lines @@
         checkReturn(String name, type) {
           var element = findElement(compiler, name);
           Expect.equals(
               type,
               simplify(
                   typesInferrer.getReturnTypeOfElement(element), closedWorld),
               name);
         }
 
         checkReturnInClass(String className, String methodName, type) {
-          var cls = findElement(compiler, className);
+          dynamic cls = findElement(compiler, className);
           var element = cls.lookupLocalMember(methodName);
           Expect.equals(
               type,
               simplify(
                   typesInferrer.getReturnTypeOfElement(element), closedWorld));
         }
 
         checkReturn('bar', commonMasks.uint31Type);
         checkReturn('baz', commonMasks.functionType);
 
         checkReturnInClass('A', 'foo', commonMasks.uint31Type);
         checkReturnInClass('B', 'foo', commonMasks.functionType);
       }));
 }