Print retraced stack-trace on test-error

Change-Id: Idfbf5d0a1d40039319b5217daf9fca29fef9e5c1
diff --git a/tools/retrace.py b/tools/retrace.py
new file mode 100755
index 0000000..3b8da1d
--- /dev/null
+++ b/tools/retrace.py
@@ -0,0 +1,15 @@
+#!/usr/bin/env python
+# Copyright (c) 2019, the R8 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.
+
+import subprocess
+import sys
+import utils
+
+def main():
+  # Run the retrace tool with standard r8lib arguments.
+  subprocess.call(['java', '-jar', utils.RETRACE_JAR, '-verbose', utils.R8LIB_JAR + '.map'])
+
+if __name__ == '__main__':
+  sys.exit(main())