Add toStructuredText to ConstantExpression and align method names with ConstantValue

pkg/compiler/lib/src/serialization/json_serializer.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.
 
 library dart2js.serialization.json;
 
 import 'dart:convert';
 import 'keys.dart';
 import 'serialization.dart';
 import 'values.dart';
@@ skipping 95 matching lines @@
     value.accept(this, indentation);
   }
 
   @override
   void visitBool(BoolValue value, String indentation) {
     buffer.write(value.value);
   }
 
   @override
   void visitConstant(ConstantValue value, String indentation) {
-    buffer.write('Constant(${value.id}):${value.constant.getText()}');
+    buffer.write('Constant(${value.id}):${value.constant.toDartText()}');
   }
 
   @override
   void visitDouble(DoubleValue value, String indentation) {
     buffer.write(value.value);
   }
 
   @override
   void visitElement(ElementValue value, String indentation) {
     buffer.write('Element(${value.id}):${value.element}');
@@ skipping 77 matching lines @@
   @override
   void visitType(TypeValue value, String indentation) {
     buffer.write('Type(${value.id}):${value.type}');
   }
 
   @override
   void visitUri(UriValue value, String indentation) {
     buffer.write('Uri(${value.value})');
   }
 }