Add --dart2js-options flag to test command

tools/testing/dart/test_suite.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.
 
 /**
  * Classes and methods for enumerating and preparing tests.
  *
  * This library includes:
  *
  * - Creating tests by listing all the Dart files in certain directories,
@@ skipping 2088 matching lines @@
   static Path get dartTestExecutable {
     var path = '$dartDir/tools/testing/bin/'
         '${Platform.operatingSystem}/dart';
     if (Platform.operatingSystem == 'windows') {
       path = '$path.exe';
     }
     return new Path(path);
   }
 
   /**
+   * Gets extra options under [key] passed to the testing script.
+   */
+  static List<String> getExtraOptions(Map configuration, String key) {
+    if (configuration[key] == null) return <String>[];
+    return configuration[key]
+        .split(" ")
+        .map((s) => s.trim())
+        .where((s) => s.isNotEmpty)
+        .toList();
+  }
+
+  /**
    * Gets extra vm options passed to the testing script.
    */
-  static List<String> getExtraVmOptions(Map configuration) {
-    var extraVmOptions = [];
-    if (configuration['vm_options'] != null) {
-      extraVmOptions = configuration['vm_options'].split(" ");
-      extraVmOptions.removeWhere((s) => s.trim() == "");
-    }
-    return extraVmOptions;
-  }
+  static List<String> getExtraVmOptions(Map configuration) =>
+      getExtraOptions(configuration, 'vm_options');
 
   static String getShortName(String path) {
     final PATH_REPLACEMENTS = const {
       "pkg_polymer_e2e_test_bad_import_test": "polymer_bi",
       "pkg_polymer_e2e_test_canonicalization_test": "polymer_c16n",
       "pkg_polymer_e2e_test_experimental_boot_test": "polymer_boot",
       "pkg_polymer_e2e_test_good_import_test": "polymer_gi",
       "tests_co19_src_Language_12_Expressions_14_Function_Invocation_":
           "co19_fn_invoke_",
       "tests_co19_src_LayoutTests_fast_dom_Document_CaretRangeFromPoint_"
@@ skipping 123 matching lines @@
  * $pass tests are expected to pass
  * $failOk tests are expected to fail that we won't fix
  * $fail tests are expected to fail that we should fix
  * $crash tests are expected to crash that we should fix
  * $timeout tests are allowed to timeout
  * $compileErrorSkip tests are skipped on browsers due to compile-time error
 """;
     print(report);
   }
 }