Use memory compiler in compiler_helper.dart.

tests/compiler/dart2js/show_package_warnings_test.dart

 // Copyright (c) 2014, 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.
 
 // Test that the '--show-package-warnings' option works as intended.
 
 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.
 const ERROR_CODE = """
 m(Object o) {
   if (o is String) {
     o = o.length;
   }
 }""";
 
@@ skipping 20 matching lines @@
   'pkg/pkg_noerror/pkg_noerror.dart': """
 import 'package:pkg_error1/pkg_error1.dart';
 import 'package:pkg_error2/pkg_error2.dart';
 """};
 
 Future test(Uri entryPoint,
             {bool showPackageWarnings: false,
              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(
       entryPoint: entryPoint,
       memorySourceFiles: SOURCE,
       options: options,
       packageRoot: Uri.parse('memory:pkg/'),
       diagnosticHandler: collector);
   print('==================================================================');
   print('test: $entryPoint showPackageWarnings=$showPackageWarnings');
@@ skipping 47 matching lines @@
         showPackageWarnings: true,
         // From package:pkg_error1 and package:pkg_error2:
         warnings: 2, hints: 2, infos: 2);
     await test(
         Uri.parse('package:pkg_noerror/pkg_noerror.dart'),
         showPackageWarnings: false,
         hints: 2 /* from summary */);
   });
 }