Late night strong mode cleaning.

tests/compiler/dart2js/inference/id_equivalence_test.dart

 // Copyright (c) 2017, 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 'dart:io';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/kernel/kernel.dart';
@@ skipping 37 matching lines @@
   Map<Id, ir.Node> irMap = <Id, ir.Node>{};
   ir.Node node = kernel.elementToIr(member);
   IrIdFinder irFinder = new IrIdFinder();
   for (Id id in expectedMap.keys.toList()) {
     ir.Node result = irFinder.find(node, id);
     if (result != null) {
       irMap[id] = result;
     }
   }
 
-  elementMap.forEach((Id id, AstElement element) {
+  elementMap.forEach((Id id, _element) {
+    AstElement element = _element;
     ir.Node irNode = irMap[id];
     Expect.equals(kernel.elementToIr(element), irNode,
         "Element mismatch on $id = $element");
     expectedMap.remove(id);
     irMap.remove(id);
   });
   astMap.forEach((Id id, ast.Node astNode) {
     ir.Node irNode = irMap[id];
     Expect.equals(
         kernel.nodeToAst[irNode], astNode, "Node mismatch on $id = $astNode");
     expectedMap.remove(id);
     irMap.remove(id);
   });
   Expect.isTrue(irMap.isEmpty, "Extra IR ids: $irMap");
 }