Add toStructuredText to ConstantExpression and align method names with ConstantValue

tests/compiler/dart2js/constant_expression_evaluate_test.dart

Index: tests/compiler/dart2js/constant_expression_evaluate_test.dart
diff --git a/tests/compiler/dart2js/constant_expression_evaluate_test.dart b/tests/compiler/dart2js/constant_expression_evaluate_test.dart
index 5fa34cc12c5088073032d3de26dc3378cf322798..60563f8e61c22e176ee272df7c29390a3ed3863b 100644
--- a/tests/compiler/dart2js/constant_expression_evaluate_test.dart
+++ b/tests/compiler/dart2js/constant_expression_evaluate_test.dart
@@ -227,10 +227,10 @@ Future testData(TestData data) async {
       Environment environment = new MemoryEnvironment(compiler, env);
       ConstantValue value =
           constant.evaluate(environment, DART_CONSTANT_SYSTEM);
-      String valueText = value.toStructuredString();
+      String valueText = value.toStructuredText();
       Expect.equals(expectedText, valueText,
           "Unexpected value '${valueText}' for contant "
-          "`${constant.getText()}`, expected '${expectedText}'.");
+          "`${constant.toDartText()}`, expected '${expectedText}'.");
     });
   });
 }