Don't use io prefix in test_suite.dart

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 1949 matching lines @@
       // Running this in a shell sucks, but rmdir is not part of the standard
       // path.
       return Process.run('rmdir', ['/s', '/q', native_path], runInShell: true)
         .then((ProcessResult result) {
           if (result.exitCode != 0) {
             throw new Exception('Can\'t delete path $native_path. '
                                 'This path might be too long');
           }  
         });
     } else {
-      var dir = new io.Directory(path);
+      var dir = new Directory(path);
       return dir.delete(recursive: true);
     }
   }
 
   static Path debugLogfile() {
     return new Path(".debug.log");
   }
 
   static String flakyFileName() {
     // If a flaky test did fail, infos about it (i.e. test name, stdin, stdout)
@@ skipping 301 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);
   }
 }