For Windows N users, they don't have default WMF installed, but users can manually install and that is what banner should do.

But currently the banner didn't show up, we should fix that and add a related test for that.

Hmm, but the test browser_decoderDoctor.js works correctly, I need to investigate that more to see what happened.

[update] because that test didn't test the part of notifying media error from a real media pipeline, which simply mocks the error and sending it to the chrome process.

The reason we didn't send any notification to the front end (in order to show the banner) is because we failed on this check, where we currently won't dispatch notificaion for any error because we didn't allow any error in our pref.

The second problem is that, even if I force to set WMF error flag, the DecoderDoctorDocumentWatcher would still notify the normal decode error, instead of the one which contains the message of WMF not found.

I need to spend more time on understanding the flow in DecoderDoctorDiagnostics.

Bug 1690661 will solve this problem, which means the infobar for WMF not found would displayed correctly. However, this works because we still load WMF decoder module in the content process, the error flag would be set. If we remove the WMF usage in the content process, then RDD/GPU won't propagate the error flag back in the content process, then we will not be able to show the infobars. Therefore, we need to implement a mechanism to propagate the error from RDD/GPU processes.

Will close this bug and file a new one for implementing the error propagation from RDD/GPU process.