Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/simple_inferrer_const_closure4_test.dart

 // Copyright (c) 2014, 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 15 matching lines @@
 """;
 
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   asyncTest(() => compiler.run(uri).then((_) {
         var typesInferrer = compiler.globalInference.typesInferrerInternal;
         var closedWorld = typesInferrer.closedWorld;
 
         checkArgument(String functionName, type) {
-          var functionElement = findElement(compiler, functionName);
+          dynamic functionElement = findElement(compiler, functionName);
           var signature = functionElement.functionSignature;
           var element = signature.requiredParameters.first;
           Expect.equals(
               type,
               simplify(typesInferrer.getTypeOfElement(element), closedWorld),
               functionName);
         }
 
         checkArgument('method', closedWorld.commonMasks.numType);
         checkArgument('returnNum', closedWorld.commonMasks.numType);
       }));
 }