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

tests/compiler/dart2js/options_helper.dart

+// Copyright (c) 2016, 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 options_helper;
+
+import 'package:compiler/src/options.dart';
+export 'package:compiler/src/options.dart';
+
+class MockDiagnosticOptions implements DiagnosticOptions {
+  const MockDiagnosticOptions();
+
+  bool get fatalWarnings => false;
+  bool get terseDiagnostics => false;
+  bool get suppressWarnings => false;
+  bool get suppressHints => false;
+  bool get showAllPackageWarnings => false;
+  bool get hidePackageWarnings => true;
+  bool showPackageWarningsFor(Uri uri) => false;
+}
+
+class MockParserOptions implements ParserOptions {
+  bool get enableConditionalDirectives => true;
+}