[ads] Error page should not trigger `NotifyTab[Text/Html]ContentDidChange`

[aseren]

Steps to Reproduce

1. Open an error webpage

Actual result:

Error webpage triggers NotifyTab[Text/Html]ContentDidChange

Expected result:

Error webpage doesn't trigger NotifyTab[Text/Html]ContentDidChange

Reproduces how often: [Easily reproduced, Intermittent Issue]

Easily reproduced