js_runtime tweaks for better code

pkg/compiler/lib/src/js_backend/constant_system_javascript.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.
 
 library dart2js.constant_system.js;
 
 import '../compiler.dart' show
     Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
@@ skipping 337 matching lines @@
    * object. It would change the prototype chain.
    */
   static const LiteralDartString PROTO_PROPERTY =
       const LiteralDartString("__proto__");
 
   /** The dart class implementing constant map literals. */
   static const String DART_CLASS = "ConstantMap";
   static const String DART_STRING_CLASS = "ConstantStringMap";
   static const String DART_PROTO_CLASS = "ConstantProtoMap";
   static const String DART_GENERAL_CLASS = "GeneralConstantMap";
-  static const String LENGTH_NAME = "length";
+  static const String LENGTH_NAME = "_length";
   static const String JS_OBJECT_NAME = "_jsObject";
   static const String KEYS_NAME = "_keys";
   static const String PROTO_VALUE = "_protoValue";
   static const String JS_DATA_NAME = "_jsData";
 
   final ListConstantValue keyList;
   final ConstantValue protoValue;
   final bool onlyStringKeys;
 
   JavaScriptMapConstant(InterfaceType type,
@@ skipping 11 matching lines @@
       result.add(keyList);
     } else {
       // Add the keys individually to avoid generating an unused list constant
       // for the keys.
       result.addAll(keys);
     }
     result.addAll(values);
     return result;
   }
 }