Use memory compiler in compiler_helper.dart.

tests/compiler/dart2js/show_package_warnings_test.dart

Index: tests/compiler/dart2js/show_package_warnings_test.dart
diff --git a/tests/compiler/dart2js/show_package_warnings_test.dart b/tests/compiler/dart2js/show_package_warnings_test.dart
index 5673032c3f4b84e2da69464f7a9e6cef8427508b..e94983c1806cf72d1087ce52fb05e7e6b7a58f50 100644
--- a/tests/compiler/dart2js/show_package_warnings_test.dart
+++ b/tests/compiler/dart2js/show_package_warnings_test.dart
@@ -7,6 +7,7 @@
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
+import 'package:compiler/src/commandline_options.dart';
 import 'memory_compiler.dart';
 
 /// Error code that creates 1 warning, 1 hint, and 1 info.
@@ -47,9 +48,9 @@ Future test(Uri entryPoint,
              int warnings: 0,
              int hints: 0,
              int infos: 0}) async {
-  var options = ['--analyze-only', '--analyze-all'];
+  var options = [Flags.analyzeOnly, Flags.analyzeAll];
   if (showPackageWarnings) {
-    options.add('--show-package-warnings');
+    options.add(Flags.showPackageWarnings);
   }
   var collector = new DiagnosticCollector();
   await runCompiler(