Remove DartString from constants.

pkg/compiler/lib/src/resolution/members.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.resolution.members;
 
 import 'package:front_end/src/fasta/scanner.dart' show isUserDefinableOperator;
 
 import '../common.dart';
 import '../common/names.dart' show Selectors;
@@ skipping 3936 matching lines @@
         Node argumentNode = node.send.arguments.head;
         ConstantExpression constant = resolver.constantCompiler
             .compileNode(argumentNode, registry.mapping);
         ConstantValue name = resolution.constants.getConstantValue(constant);
         if (!name.isString) {
           ResolutionDartType type = name.getType(commonElements);
           reporter.reportErrorMessage(
               argumentNode, MessageKind.STRING_EXPECTED, {'type': type});
         } else {
           StringConstantValue stringConstant = name;
-          String nameString = stringConstant.toDartString().slowToString();
+          String nameString = stringConstant.primitiveValue;
           if (validateSymbol(argumentNode, nameString)) {
             registry.registerConstSymbol(nameString);
           }
         }
       } else if (commonElements.isMirrorsUsedConstructor(constructor)) {
         resolution.mirrorUsageAnalyzerTask.validate(node, registry.mapping);
       }
 
       analyzeConstantDeferred(node);
 
@@ skipping 834 matching lines @@
     }
     return const NoneResult();
   }
 }
 
 /// Looks up [name] in [scope] and unwraps the result.
 Element lookupInScope(
     DiagnosticReporter reporter, Node node, Scope scope, String name) {
   return Elements.unwrap(scope.lookup(name), reporter, node);
 }