Add toStructuredText to ConstantExpression and align method names with ConstantValue

pkg/compiler/lib/src/serialization/values.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.
 
 /// Class hiarchy for semantic wrapping of serializable values.
 
 library dart2js.serialization.values;
 
 import '../constants/expressions.dart';
 import '../dart_types.dart';
@@ skipping 49 matching lines @@
 }
 
 class ConstantValue implements Value {
   final ConstantExpression constant;
   final Value id;
 
   ConstantValue(this.constant, this.id);
 
   accept(ValueVisitor visitor, arg) => visitor.visitConstant(this, arg);
 
-  String toString() => constant.getText();
+  String toString() => constant.toDartText();
 }
 
 abstract class PrimitiveValue implements Value {
   get value;
 
   String toString() => value.toString();
 }
 
 class BoolValue extends PrimitiveValue {
   final bool value;
@@ skipping 88 matching lines @@
   R visitBool(BoolValue value, A arg);
   R visitInt(IntValue value, A arg);
   R visitDouble(DoubleValue value, A arg);
   R visitString(StringValue value, A arg);
   R visitObject(ObjectValue value, A arg);
   R visitMap(MapValue value, A arg);
   R visitList(ListValue value, A arg);
   R visitEnum(EnumValue value, A arg);
   R visitUri(UriValue value, A arg);
 }