Print out experimental test.py reproduction command

tools/testing/dart/utils.dart

Index: tools/testing/dart/utils.dart
diff --git a/tools/testing/dart/utils.dart b/tools/testing/dart/utils.dart
index 4c8170f9125ab308b7c7fff9ba5fab3b96a7381b..3ddf330b75bf8e91b047e74abf5d4fa9c9310037 100644
--- a/tools/testing/dart/utils.dart
+++ b/tools/testing/dart/utils.dart
@@ -75,3 +75,12 @@ String decodeUtf8(List<int> bytes) {
   return utf.decodeUtf8(bytes);
 }
 
+// This function is pretty stupid and only puts quotes around an argument if
+// it the argument contains a space.
+String escapeCommandLineArgument(String argument) {
+  if (argument.contains(' ')) {
+    return '"$argument"';
+  }
+  return argument;
+}
+