Handle Native("...") annotations in KernelBehaviorBuilder.

pkg/compiler/lib/src/kernel/elements.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.
 
 /// Entity model for elements derived from Kernel IR.
 
 import '../elements/elements.dart';
 import '../elements/entities.dart';
 
 class KLibrary implements LibraryEntity {
@@ skipping 138 matching lines @@
   @override
   bool get isAssignable => true;
 
   @override
   bool get isSetter => true;
 
   String get _kind => 'setter';
 }
 
 class KField extends KMember implements FieldEntity {
+  /// Field index used for fast lookup in [KernelWorldBuilder].
+  final int fieldIndex;
   final bool isAssignable;
 
-  KField(KClass enclosingClass, Name name, {bool isStatic, this.isAssignable})
+  KField(this.fieldIndex, KClass enclosingClass, Name name,
+      {bool isStatic, this.isAssignable})
       : super(enclosingClass, name, isStatic: isStatic);
 
   @override
   bool get isField => true;
 
   String get _kind => 'field';
 }
 
 class KTypeVariable implements TypeVariableEntity {
   final Entity typeDeclaration;
   final String name;
   final int index;
 
   KTypeVariable(this.typeDeclaration, this.name, this.index);
 
   String toString() => 'type_variable(${typeDeclaration.name}.$name)';
 }
 
 class KLocalFunction implements Local {
   final String name;
   final MemberEntity memberContext;
   final Entity executableContext;
 
   KLocalFunction(this.name, this.memberContext, this.executableContext);
 
   String toString() =>
       'local_function(${memberContext.name}.${name ?? '<anonymous>'})';
 }