Lighthouse doesn't exclude Chrome extensions from audit

[MonsieurLeSuisse]

Provide the steps to reproduce

1. Install/activate Google Dictionary extension in Google Chrome
2. Open Chrome developer tools
3. Run LH on any url, run Audits (Best Practices test is enough)
4. Check result in Best Practices section.
5. See warning "Uses deprecated API's" ... "Element.createShadowRoot is deprecated and will be removed in ..."
6. Hover over entry in URL column, it reveals: chrome-extension://xyz/content.min.js which belongs to the Google Dictionary extension.

What is the current behavior?

LH processes all JS even that of chrome extensions. This falsifies the result of an website audit.

What is the expected behavior?

Lighthouse in Chrome Audits is used to check websites. Therefore it must avoid chrome extensions from being included in the audit.

Environment Information

• Affected Channels: Extension, DevTools
• Lighthouse version: Lighthouse 3.0.3
• Operating System: Windows 10
• Chome: Version 70.0.3538.102 (Official Build) (64-Bit)

[patrickhulce]

Thanks for filing @MonsieurLeSuisse! We consider this a duplicate of #4516, see more discussion in #5792.