Print out experimental test.py reproduction command

tools/testing/dart/test_runner.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 executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 98 matching lines @@
   String commandLine;
 
   Command(this.executable, this.arguments, [this.environment = null]) {
     if (io.Platform.operatingSystem == 'windows') {
       // Windows can't handle the first command if it is a .bat file or the like
       // with the slashes going the other direction.
       // TODO(efortuna): Remove this when fixed (Issue 1306).
       executable = executable.replaceAll('/', '\\');
     }
     var quotedArguments = [];
-    arguments.forEach((argument) => quotedArguments.add('"$argument"'));
-    commandLine = "\"$executable\" ${quotedArguments.join(' ')}";
+    quotedArguments.add(escapeCommandLineArgument(executable));
+    quotedArguments.addAll(arguments.map(escapeCommandLineArgument));
+    commandLine = quotedArguments.join(' ');
   }
 
   String toString() => commandLine;
 
   Future<bool> get outputIsUpToDate => new Future.immediate(false);
   io.Path get expectedOutputFile => null;
   bool get isPixelTest => false;
 }
 
 class CompilationCommand extends Command {
@@ skipping 1779 matching lines @@
     }
   }
 
   void eventAllTestsDone() {
     for (var listener in _eventListener) {
       listener.allDone();
     }
   }
 }