Fix the pubspec and warnings in pkg/kernel.

pkg/kernel/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';
 import '../transformations/flags.dart';
 import 'analyzer.dart';
 import 'loader.dart';
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/parser.dart';
 import 'package:analyzer/src/dart/element/member.dart';
+import 'package:analyzer/src/error/codes.dart';
 
 /// Provides reference-level access to libraries, classes, and members.
 ///
 /// "Reference level" objects are incomplete nodes that have no children but
 /// can be used for linking until the loader promotes the node to a higher
 /// loading level.
 ///
 /// The [ReferenceScope] is the most restrictive scope in a hierarchy of scopes
 /// that provide increasing amounts of contextual information.  [TypeScope] is
 /// used when type parameters might be in scope, and [MemberScope] is used when
@@ skipping 2775 matching lines @@
     if (list[i - 1].compareTo(item) == 0) {
       ++deleted;
     } else if (deleted > 0) {
       list[i - deleted] = item;
     }
   }
   if (deleted > 0) {
     list.length -= deleted;
   }
 }