Print out experimental test.py reproduction command

tools/testing/dart/test_runner.dart

Index: tools/testing/dart/test_runner.dart
diff --git a/tools/testing/dart/test_runner.dart b/tools/testing/dart/test_runner.dart
index 63c8164c0aac294189561dbb3a1693535163a17d..73c9cba04c25affcc6683ff3a7c55354d7866597 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -116,8 +116,9 @@ class Command {
       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;