Remove DartString from constants.

pkg/compiler/lib/src/ssa/nodes.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.
 
 import '../closure.dart';
 import '../common.dart';
 import '../common_elements.dart' show CommonElements;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
 import '../elements/elements.dart' show JumpTarget, LabelDefinition;
 import '../elements/entities.dart';
 import '../elements/types.dart';
 import '../io/source_information.dart';
 import '../js/js.dart' as js;
 import '../js_backend/js_backend.dart';
 import '../native/native.dart' as native;
-import '../tree/dartstring.dart' as ast;
 import '../types/constants.dart' show computeTypeMask;
 import '../types/types.dart';
 import '../universe/selector.dart' show Selector;
 import '../universe/side_effects.dart' show SideEffects;
 import '../util/util.dart';
 import '../world.dart' show ClosedWorld;
 import 'invoke_dynamic_specializers.dart';
 import 'validate.dart';
 
 abstract class HVisitor<R> {
@@ skipping 258 matching lines @@
   }
 
   HConstant addConstantInt(int i, ClosedWorld closedWorld) {
     return addConstant(closedWorld.constantSystem.createInt(i), closedWorld);
   }
 
   HConstant addConstantDouble(double d, ClosedWorld closedWorld) {
     return addConstant(closedWorld.constantSystem.createDouble(d), closedWorld);
   }
 
-  HConstant addConstantString(ast.DartString str, ClosedWorld closedWorld) {
+  HConstant addConstantString(String str, ClosedWorld closedWorld) {
     return addConstant(
         closedWorld.constantSystem.createString(str), closedWorld);
   }
 
   HConstant addConstantStringFromName(js.Name name, ClosedWorld closedWorld) {
     return addConstant(
         new SyntheticConstantValue(
             SyntheticConstantKind.NAME, js.quoteName(name)),
         closedWorld);
   }
@@ skipping 3237 matching lines @@
   // ignore: MISSING_RETURN
   String get kindAsString {
     switch (kind) {
       case TypeInfoExpressionKind.COMPLETE:
         return 'COMPLETE';
       case TypeInfoExpressionKind.INSTANCE:
         return 'INSTANCE';
     }
   }
 }