This feature will autoupgrade optionally-blockable mixed content (HTTP content in HTTPS sites) by rewriting the URL to HTTPS, without a fallback to HTTP if the content is not available over HTTPS. Image mixed content autoupgrades by default are targeted for M86. Audio/Video mixed content autoupgrades are separately tracked in https://www.chromestatus.com/feature/5557268741357568
Docs: https://docs.google.com/document/d/1dp-kuN25wnEbMPNWBxM8LvOjyeydWpXPklNnGcsWK1o/edit