Fix some strong mode issues.

lib/analyzer/ast_from_analyzer.dart

 // Copyright (c) 2016, 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.
 library kernel.analyzer.ast_from_analyzer;
 
 import '../ast.dart' as ast;
 import '../frontend/accessors.dart';
 import '../frontend/super_initializers.dart';
 import '../log.dart';
 import '../type_algebra.dart';
@@ skipping 2408 matching lines @@
 
   /// True for the `index` field of an `enum` class.
   static bool _isIndexField(FieldElement field) => field.name == 'index';
 
   visitEnumDeclaration(EnumDeclaration node) {
     addAnnotations(node.metadata);
     ast.Class classNode = currentClass;
     var intType =
         new ast.InterfaceType(scope.loader.getCoreClassReference('int'));
     var indexFieldElement = element.fields.firstWhere(_isIndexField);
-    var indexField = scope.getMemberReference(indexFieldElement);
+    ast.Field indexField = scope.getMemberReference(indexFieldElement);
     indexField.type = intType;
     classNode.addMember(indexField);
     var parameter = new ast.VariableDeclaration('index', type: intType);
     var function = new ast.FunctionNode(new ast.EmptyStatement(),
         positionalParameters: [parameter]);
     var superConstructor = scope.loader.getRootClassConstructorReference();
     var constructor = new ast.Constructor(function,
         name: new ast.Name(''),
         isConst: true,
         initializers: [
@@ skipping 332 matching lines @@
   if (element is FieldElement) return element.getter;
   return element;
 }
 
 Element desynthesizeSetter(Element element) {
   if (element == null || !element.isSynthetic) return element;
   if (element is PropertyAccessorElement) return element.variable;
   if (element is FieldElement) return element.setter;
   return element;
 }