Refactor ConstantSystem

pkg/compiler/lib/src/js_backend/backend_helpers.dart

 // Copyright (c) 2015, 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.js_backend.helpers;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers, Uris;
 import '../compiler.dart' show Compiler;
 import '../core_types.dart' show CommonElements, ElementEnvironment;
@@ skipping 423 matching lines @@
       new Selector.call(const PublicName('validated'), CallStructure.ONE_ARG);
 
   ConstructorEntity get symbolValidatedConstructor =>
       _symbolValidatedConstructor ??= _findConstructor(
           symbolImplementationClass, symbolValidatedConstructorSelector.name);
 
   ClassEntity _symbolImplementationClass;
   ClassEntity get symbolImplementationClass =>
       _symbolImplementationClass ??= _findClass(internalLibrary, 'Symbol');
 
+  FieldEntity _symbolImplementationField;
+
+  /// Returns the field that holds the internal name in the implementation class
+  /// for `Symbol`.
+  FieldEntity get symbolImplementationField => _symbolImplementationField ??=
+      _env.lookupClassMember(symbolImplementationClass, '_name',
+          required: true);
+
   ConstructorEntity _symbolValidatedConstructor;
 
   bool isSymbolValidatedConstructor(ConstructorEntity element) {
     if (_symbolValidatedConstructor != null) {
       return element == _symbolValidatedConstructor;
     }
     return false;
   }
 
   ConstructorEntity _mapLiteralConstructor;
@@ skipping 326 matching lines @@
   ClassEntity get annotationReturnsClass => _findHelperClass('Returns');
 
   ClassEntity get annotationJSNameClass => _findHelperClass('JSName');
 
   FunctionEntity get toStringForNativeObject =>
       _findHelperFunction('toStringForNativeObject');
 
   FunctionEntity get hashCodeForNativeObject =>
       _findHelperFunction('hashCodeForNativeObject');
 }