Add toStructuredText to ConstantExpression and align method names with ConstantValue

tests/compiler/dart2js/resolver_test.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 'dart:async';
 import 'dart:collection';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/constants/expressions.dart';
@@ skipping 1051 matching lines @@
   return Future.forEach(testedConstants.keys, (String constant) {
     return MockCompiler.create((MockCompiler compiler) {
       CollectingTreeElements elements =
           compiler.resolveStatement("main() => $constant;");
       List<String> expectedConstants = testedConstants[constant];
       DiagnosticCollector collector = compiler.diagnosticCollector;
       Expect.equals(0, collector.warnings.length);
       Expect.equals(0, collector.errors.length);
       List<ConstantExpression> constants = elements.constants;
       String constantsText =
-          '[${constants.map((c) => c.getText()).join(', ')}]';
+          '[${constants.map((c) => c.toDartText()).join(', ')}]';
       Expect.equals(expectedConstants.length, constants.length,
           "Expected ${expectedConstants.length} constants for `${constant}` "
           "found $constantsText.");
       for (int index = 0; index < expectedConstants.length; index++) {
-        Expect.equals(expectedConstants[index], constants[index].getText(),
+        Expect.equals(expectedConstants[index], constants[index].toDartText(),
             "Expected ${expectedConstants} for `$constant`, "
             "found $constantsText.");
       }
     });
   });
 }
 
 map(ResolverVisitor visitor) {
   CollectingTreeElements elements = visitor.registry.mapping;
   return elements.map;
@@ skipping 353 matching lines @@
     }
     main() => A.m();
   ''', functionName: 'm');
   check('''
     class A {
       m() => () => await - 3;
     }
     main() => new A().m();
   ''', className: 'A');
 }