dart2js: Use an abstract Name class for names in the generated JavaScript ast.

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 '../constants/constant_system.dart';
 import '../constants/values.dart';
 import '../constant_system_dart.dart';
 import '../dart_types.dart';
@@ skipping 236 matching lines @@
 
   NumConstantValue createInt32(int i) => new IntConstantValue(i & BITS32);
   NumConstantValue createDouble(double d)
       => convertToJavaScriptConstant(new DoubleConstantValue(d));
   StringConstantValue createString(DartString string) {
     return new StringConstantValue(string);
   }
   BoolConstantValue createBool(bool value) => new BoolConstantValue(value);
   NullConstantValue createNull() => new NullConstantValue();
 
-
   @override
   ListConstantValue createList(InterfaceType type,
                                List<ConstantValue> values) {
     return new ListConstantValue(type, values);
   }
 
   @override
   ConstantValue createType(Compiler compiler, DartType type) {
     return new TypeConstantValue(
         type, compiler.backend.typeImplementation.computeType(compiler));
@@ skipping 106 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;
   }
 }