Remove DartString from constants.

pkg/compiler/lib/src/resolution/resolution_strategy.dart

 // Copyright (c) 2017, 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_strategy;
 
 import '../common.dart';
 import '../common_elements.dart';
 import '../common/backend_api.dart';
 import '../common/names.dart';
@@ skipping 501 matching lines @@
         ConstantValue constant =
             _compiler.constants.getConstantValue(annotation.constant);
         if (constant == null || constant is! ConstructedConstantValue) continue;
         ConstructedConstantValue constructedConstant = constant;
         if (constructedConstant.type.element ==
             _commonElements.jsAnnotationClass) {
           ConstantValue value = constructedConstant.fields[nameField];
           String name;
           if (value.isString) {
             StringConstantValue stringValue = value;
-            name = stringValue.primitiveValue.slowToString();
+            name = stringValue.primitiveValue;
           } else {
             // TODO(jacobr): report a warning if the value is not a String.
             name = '';
           }
           return name;
         }
       }
       return null;
     }
 
@@ skipping 102 matching lines @@
             }
           }
         });
       });
     }
 
     _compiler.libraryLoader.libraries
         .forEach(processJsInteropAnnotationsInLibrary);
   }
 }