Extension Error: Cannot attach to this target.

[ghost]

Lighthouse Version: 3.1.1
Lighthouse Commit: 44dcc5d
Chrome Version: 69.0.3497.95
Initial URL: https://mail.google.com/mail/ca/u/0/#inbox
Error Message: Cannot attach to this target.
Stack Trace:

Error: Cannot attach to this target.
    at Object.chrome.debugger.attach [as callback] (chrome-extension://blipmdconlkpinefehnmjammfjpmpbjk/scripts/lighthouse-ext-background.js:17916:15)
    at safeCallbackApply (extensions::uncaught_exception_handler:27:15)
    at handleResponse (extensions::sendRequest:67:7)

[wardpeet]

duping into #5798