Finish strong mode cleaning of dart2js.

pkg/compiler/lib/src/universe/element_world_builder.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.
 
 part of world_builder;
 
 /// [ResolutionEnqueuerWorldBuilder] based on the [Element] model.
 class ElementResolutionWorldBuilder extends ResolutionWorldBuilderBase {
   /// Used for testing the new more precise computation of instantiated types
   /// and classes.
@@ skipping 45 matching lines @@
 
     Map<ClassEntity, InstantiationInfo> instantiationMap =
         <ClassEntity, InstantiationInfo>{};
 
     InstantiationInfo infoFor(ClassEntity cls) {
       return instantiationMap.putIfAbsent(cls, () => new InstantiationInfo());
     }
 
     _instantiationInfo.forEach((cls, info) {
       if (info.instantiationMap != null) {
-        info.instantiationMap
-            .forEach((ConstructorElement constructor, Set<Instance> set) {
+        info.instantiationMap.forEach((_constructor, Set<Instance> set) {
+          ConstructorElement constructor = _constructor;
           for (Instance instance in set) {
             if (instance.isRedirection) {
               continue;
             }
             if (constructor == null || !constructor.isRedirectingFactory) {
               infoFor(cls)
                   .addInstantiation(constructor, instance.type, instance.kind);
             } else {
               ConstructorElement target = constructor.effectiveTarget;
               ResolutionInterfaceType targetType =
@@ skipping 111 matching lines @@
         classSets: _classSets);
   }
 
   @override
   void registerMixinUse(
       MixinApplicationElement mixinApplication, ClassElement mixin) {
     assert(mixin.isDeclaration);
     super.registerMixinUse(mixinApplication, mixin);
   }
 }