Remove DartString from constants.

pkg/compiler/lib/src/native/behavior.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.
 
 import '../common.dart';
 import '../common/backend_api.dart' show ForeignResolver;
 import '../common/resolution.dart' show ParsingContext, Resolution;
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../common_elements.dart' show CommonElements;
@@ skipping 879 matching lines @@
       ConstructedConstantValue constructedObject = value;
       if (constructedObject.type.element != annotationClass) continue;
 
       Iterable<ConstantValue> fields = constructedObject.fields.values;
       // TODO(sra): Better validation of the constant.
       if (fields.length != 1 || !fields.single.isString) {
         reporter.internalError(CURRENT_ELEMENT_SPANNABLE,
             'Annotations needs one string: ${value.toStructuredText()}');
       }
       StringConstantValue specStringConstant = fields.single;
-      String specString = specStringConstant.toDartString().slowToString();
+      String specString = specStringConstant.primitiveValue;
       for (final typeString in specString.split('|')) {
         var type = NativeBehavior._parseType(typeString, lookupType);
         if (types == null) types = [];
         types.add(type);
       }
     }
     return types;
   }
 
   /// Models the behavior of having intances of [type] escape from Dart code
@@ skipping 134 matching lines @@
   @override
   bool get trustJSInteropTypeAnnotations =>
       compiler.options.trustJSInteropTypeAnnotations;
 
   @override
   DiagnosticReporter get reporter => compiler.reporter;
 
   @override
   Resolution get resolution => compiler.resolution;
 }