Port code at https://searchfox.org/mozilla-central/rev/5a4aaccb28665807a6fd49cf48367d47fbb5a19a/browser/base/content/browser-media.js#213-424 + https://searchfox.org/mozilla-central/rev/5a4aaccb28665807a6fd49cf48367d47fbb5a19a/browser/modules/ContentObservers.js#39-45 to use new Fission compatible actors

What is the user-facing effect of this? We need this to triage for Fission priority.

(In reply to Neha Kochar [:neha] from comment #1)

What is the user-facing effect of this? We need this to triage for Fission priority.

Diagnostic information relating to media handling failures in gecko. I do not know the full extent and hope to get a better idea once I've picked this task up. As an example, one of the things I believe this does is show a notification for the case where we believe users do not have Windows codecs installed. That notification helps guide users towards installing the appropriate codec pack so we can then use Windows' decoding for proprietary codecs.

Tracking for Fission M7 Beta. We should fix these Windows codec notifications before we ship Fission, but they probably don't need to block enabling Fission in Nightly (M6). Most Nightly users probably keep their systems up to date and have the necessary codecs installed.

Port handling of DecoderDoctor notifications for fission. This is done by moving
the observing of 'decoder-doctor-notification' from browser-media.js to fission
friendly actors.

As browser-media.js had only code related to this patch left it is removed along
with references to it.

Expand the decoder doctor browser chrome test to check that notifications
trigger the expected UI behaviour when sent from cross origin iframes.

https://hg.mozilla.org/mozilla-central/rev/06da457da734
https://hg.mozilla.org/mozilla-central/rev/4bb25142d23c