Add toStructuredText to ConstantExpression and align method names with ConstantValue

pkg/compiler/lib/src/dart_backend/backend_ast_nodes.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.
 
 library backend_ast_nodes;
 
 import '../constants/values.dart' as values;
 import '../dart_types.dart' as types;
 import '../elements/elements.dart' as elements;
 import '../tree/tree.dart' as tree;
@@ skipping 834 matching lines @@
             write('-1/0.0');
           });
         } else if (v.isNaN) {
           withPrecedence(MULTIPLICATIVE, () {
             write('0/0.0');
           });
         } else {
           write(v.toString());
         }
       } else {
-        write(e.value.unparse());
+        write(e.value.toDartText());
       }
     } else if (e is LiteralList) {
       if (e.isConst) {
         write(' const ');
       }
       if (e.typeArgument != null) {
         write('<');
         writeType(e.typeArgument);
         write('>');
       }
@@ skipping 681 matching lines @@
   final StringChunk previous;
   final tree.StringQuoting quoting;
   num cost;
 
   OpenStringChunk(this.previous, this.quoting, this.cost);
 
   StringChunk end(int endIndex) {
     return new StringChunk(previous, quoting, endIndex);
   }
 }