dart2js: Support const symbols in the startup emitter.

pkg/compiler/lib/src/js_emitter/model.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 dart2js.new_js_emitter.model;
 
 import '../js/js.dart' as js show Expression, Statement, Name, Literal,
     TokenFinalizer;
 import '../constants/values.dart' show ConstantValue;
 
 import '../deferred_load.dart' show OutputUnit;
 
 import 'js_emitter.dart' show MetadataCollector, TokenFinalizer;
 
 import '../common.dart';
 
 class Program {
   final List<Fragment> fragments;
   final List<Holder> holders;
   final bool outputContainsConstantList;
   final bool needsNativeSupport;
   final bool hasIsolateSupport;
   /// A map from load id to the list of fragments that need to be loaded.
   final Map<String, List<Fragment>> loadMap;
+  /// A map from names to strings.
+  ///
+  /// This map is needed to support `const Symbol` expressions;
+  final Map<js.Name, String> symbolsMap;
 
   // If this field is not `null` then its value must be emitted in the embedded
   // global `TYPE_TO_INTERCEPTOR_MAP`. The map references constants and classes.
   final js.Expression typeToInterceptorMap;
 
   // TODO(floitsch): we should store the metadata directly instead of storing
   // the collector. However, the old emitter still updates the data.
   final MetadataCollector _metadataCollector;
   final Iterable<js.TokenFinalizer> finalizers;
 
   Program(this.fragments,
           this.holders,
           this.loadMap,
+          this.symbolsMap,
           this.typeToInterceptorMap,
           this._metadataCollector,
           this.finalizers,
           {this.needsNativeSupport,
            this.outputContainsConstantList,
            this.hasIsolateSupport}) {
     assert(needsNativeSupport != null);
     assert(outputContainsConstantList != null);
     assert(hasIsolateSupport != null);
   }
@@ skipping 464 matching lines @@
               functionType: functionType);
 
   bool get isStatic => true;
 }
 
 class StaticStubMethod extends StubMethod implements StaticMethod {
   Holder holder;
   StaticStubMethod(js.Name name, this.holder, js.Expression code)
       : super(name, code);
 }