Redo "Construct literal maps using factory constructor."

tests/compiler/dart2js/dart_backend_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/compiler.dart';
@@ skipping 15 matching lines @@
 class Function {}
 class List<T> {}
 class Map<K,V> {}
 class BoundClosure {}
 class Closure {}
 class Dynamic_ {}
 class Null {}
 class TypeError {}
 class Type {}
 class StackTrace {}
-class LinkedHashMap {}
+class LinkedHashMap {
+  factory LinkedHashMap._empty() => null;
+  factory LinkedHashMap._literal(elements) => null;
+}
 class Math {
   static double parseDouble(String s) => 1.0;
 }
 print(x) {}
 identical(a, b) => true;
 const proxy = 0;
 ''';
 
 const ioLib = r'''
 library io;
@@ skipping 684 matching lines @@
   testStaticAccessIoLib();
   testLocalFunctionPlaceholder();
   testMinification();
   testClosureLocalsMinified();
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
   testUnresolvedNamedConstructor();
 }