In test.dart, don't check that the shell or compiler executable exists if we are just listing tests.

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.
 
 #library("test_suite");
 
 #import("dart:io");
 #import("status_file_parser.dart");
 #import("test_runner.dart");
 #import("multitest.dart");
@@ skipping 946 matching lines @@
       case 'frogium':
       case 'webdriver':
         return 'frog/bin/frogsh$suffix';
       default:
         throw "Unknown compiler for: ${configuration['component']}";
     }
   }
 
   static String dartShellFileName(Map configuration) {
     var name = '${buildDir(configuration)}/${executableName(configuration)}';
-    if (!(new File(name)).existsSync()) {
+    if (!(new File(name)).existsSync() && !configuration['list']) {
       throw "Executable '$name' does not exist";
     }
     return name;
   }
 
   static String compilerPath(Map configuration) {
     if (configuration['component'] == 'dartium') {
       return null;  // No separate compiler for dartium tests.
     }
     var name = configuration['frog'];
     if (name == '') {
       name = '${buildDir(configuration)}/${compilerName(configuration)}';
     }
-    if (!(new File(name)).existsSync()) {
+    if (!(new File(name)).existsSync() && !configuration['list']) {
       throw "Executable '$name' does not exist";
     }
     return name;
   }
 
   static String outputDir(Map configuration) {
     var outputDir = '';
     var system = configuration['system'];
     if (system == 'linux') {
       outputDir = 'out/';
@@ skipping 79 matching lines @@
  * $noCrash tests are expected to be flaky but not crash
  * $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
 """;
     print(report);
    }
 }