I am unclear on whether the XSS Auditor attempts to sanitize navigations of this form (e.g. localhost, not cross-origin); I don't think the repro script looks very interesting, and the <SCRIPT> is plainly in the request URL.

As a "best effort" feature, XSS Auditor bypasses are not considered security bugs; changing bug type. https://www.chromium.org/Home/chromium-security/security-faq#TOC-Are-XSS-filter-bypasses-considered-security-bugs-

Hi, what would be helpful for me is rather than trying to run your PHP script, would be if you could provide me with:

The portion of the URL containing the XSS payload, and
The output from the server (e.g. view-source) that invokes the script.

Looking at the PHP man page for print_r(), it's going to introduce stray punctuation (e.g. the => in "[x] => y") that wasn't in the original input.  XSSAuditor can't guard against every possible transformation, and I don't think this is one we want to cover.

Still looking at var_export.

Ditto with var_export(), it introduces "=>" in the middle of the expression.  

I think that we're going to choose not to cover these particular server-side transformations.