unable to tell which report triggered _onWriteReport()

can we also pass the reporter to this function?

it's handy to know what report was just written esp when the path is dynamic based on the browser name. I can hook up a PR if that sounds okay.

Start by locating _onWriteReport() and trace where reports are written, especially when the output path depends on the browser name. Update the function interface so the reporter is available there, and verify that callers still work and the written report can be identified.

Written by the indexing model from the issue text.