McJordan

+1 This would indeed be very useful in order to get an accurate code coverage report.

The [@web/test-runner-coverage-v8](https://github.com/modernweb-dev/web/blob/master/packages/test-runner-coverage-v8/src/index.ts#L3) package uses [the v8-to-istanbul lib which initializes `all` to false](https://github.com/istanbuljs/v8-to-istanbul/blob/master/lib/v8-to-istanbul.js#L43).

Relates to #1873

@aomarks, @bicknellr, this is a pretty significant bug because it prevents us from using the native feature set of `toggleAttribute`. Let me know how I can help expedite this merge...

@jpzwarte Apologies for the delay! I've addressed the comments that were left

@bicknellr Thank you for the review and my apologies for the tardiness of my response. I've addressed your comments. Let me know if it requires additional changes or tests

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