Restrict backend misuse

tests/compiler/dart2js/mock_libraries.dart

 // Copyright (c) 2014, 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 for creating mock versions of platform and internal libraries.
 
 library mock_libraries;
 
 const DEFAULT_PLATFORM_CONFIG = """
 [libraries]
@@ skipping 46 matching lines @@
   'Iterable': '''
       abstract class Iterable<E> {
           Iterator<E> get iterator => null;
       }''',
   'Iterator': '''
       abstract class Iterator<E> {
           E get current => null;
       }''',
   'LinkedHashMap': r'''
       class LinkedHashMap<K, V> implements Map<K, V> {
-        factory LinkedHashMap._empty() => null;
-        factory LinkedHashMap._literal(elements) => null;
-        static _makeEmpty() => null;
-        static _makeLiteral(elements) => null;
       }''',
   'List': r'''
       class List<E> extends Iterable<E> {
         var length;
         List([length]);
         List.filled(length, element);
         E get first => null;
         E get last => null;
         E get single => null;
         E removeLast() => null;
@@ skipping 25 matching lines @@
   'Symbol': 'class Symbol { final name; const Symbol(this.name); }',
   'Type': 'class Type {}',
   'Pattern': 'abstract class Pattern {}',
 };
 
 const String DEFAULT_PATCH_CORE_SOURCE = r'''
 import 'dart:_js_helper';
 import 'dart:_interceptors';
 import 'dart:_isolate_helper';
 import 'dart:async';
+
+@patch
+class LinkedHashMap<K, V> {
+  factory LinkedHashMap._empty() => null;
+  factory LinkedHashMap._literal(elements) => null;
+  static _makeEmpty() => null;
+  static _makeLiteral(elements) => null;
+}
 ''';
 
 const Map<String, String> DEFAULT_JS_HELPER_LIBRARY = const <String, String>{
   'assertTest': 'assertTest(a) {}',
   'assertThrow': 'assertThrow(a) {}',
   'assertHelper': 'assertHelper(a) {}',
   'assertUnreachable': 'assertUnreachable() {}',
   'assertIsSubtype': 'assertIsSubtype(subtype, supertype, message) {}',
   'assertSubtype': 'assertSubtype(object, isField, checks, asField) {}',
   'assertSubtypeOfRuntimeType': 'assertSubtypeOfRuntimeType(object, type) {}',
@@ skipping 330 matching lines @@
 
     const LookupMap(this._entries, [this._nestedMaps = const []])
         : _key = null, _value = null;
 
     const LookupMap.pair(this._key, this._value)
         : _entries = const [], _nestedMaps = const [];
     V operator[](K k) => null;
   }''',
   '_version': 'const _version = "0.0.1+1";',
 };