Repeats and fixes the changes landed & reverted as CL 1789553003.

tests/compiler/dart2js/unparser2_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 "package:expect/expect.dart";
 import "package:compiler/src/parser/element_listener.dart";
 import "package:compiler/src/parser/node_listener.dart";
 import "package:compiler/src/parser/parser.dart";
 import "package:compiler/src/scanner/string_scanner.dart";
 import "package:compiler/src/tokens/token.dart";
 import "package:compiler/src/tree/tree.dart";
 
 import "package:compiler/src/diagnostics/diagnostic_listener.dart";
 import "package:compiler/src/elements/elements.dart"
     show CompilationUnitElement,
          LibraryElement;
 import "package:compiler/src/elements/modelx.dart"
     show CompilationUnitElementX,
          LibraryElementX;
 import "package:compiler/src/script.dart";
 
+import "options_helper.dart";
+
 main() {
   testClassDef();
   testClass1Field();
   testClass2Fields();
   testClass1Field1Method();
   testClass1Field2Method();
   testClassDefTypeParam();
   testEnumDef();
   testEnum1Value();
   testEnum2Value();
@@ skipping 45 matching lines @@
   compareCode('enum T {A,B,C,}', expectedResult: 'enum T {A,B,C}');
 }
 
 void compareCode(String code, {String expectedResult}) {
   if (expectedResult == null) {
     expectedResult = code;
   }
   Expect.equals(expectedResult, doUnparse(code));
 }
 
-
 String doUnparse(String source) {
   MessageCollector diagnosticListener = new MessageCollector();
   Script script = new Script(null, null, null);
   LibraryElement lib = new LibraryElementX(script);
   CompilationUnitElement element = new CompilationUnitElementX(script, lib);
   StringScanner scanner = new StringScanner.fromString(source);
   Token beginToken = scanner.tokenize();
   NodeListener listener = new NodeListener(
       const ScannerOptions(), diagnosticListener, element);
-  Parser parser = new Parser(listener);
+  Parser parser = new Parser(listener, new MockParserOptions());
   parser.parseUnit(beginToken);
   Node node = listener.popNode();
   Expect.isTrue(listener.nodes.isEmpty);
   return unparse(node);
 }
 
 class MessageCollector extends DiagnosticReporter {
   List<String> messages;
   MessageCollector() {
     messages = [];
   }
   void internalError(node, String reason) {
     messages.add(reason);
     throw reason;
   }
 
   void log(message) {
     messages.add(message);
   }
 
   noSuchMethod(Invocation invocation) => throw 'unsupported operation';
 }