I think this will be similar to the DidComposite message (bug 1333968). We'll need to figure out which tab the message and then send the message to the event target for that TabGroup. For the first part, I think we can get the right TabChild via the APZChild's mController->mBrowser (assuming it's a ContentProcessController). For the second part, bug 1333968 describes the two possible solutions.

(In reply to Bill McCloskey (:billm) from comment #0) > For the first part, I think we can get the right TabChild via the APZChild's > mController->mBrowser (assuming it's a ContentProcessController). Yes, for messages going to the content process, the mController on the APZChild side will be a ContentProcessController, and the mBrowser is the TabChild. Is there something you need us ("APZ folks") to do here, or is this something you will implement? I haven't been following the TabGroup changes.

(In reply to Kartikaya Gupta (email:kats@mozilla.com) from comment #1) > (In reply to Bill McCloskey (:billm) from comment #0) > > For the first part, I think we can get the right TabChild via the APZChild's > > mController->mBrowser (assuming it's a ContentProcessController). > > Yes, for messages going to the content process, the mController on the > APZChild side will be a ContentProcessController, and the mBrowser is the > TabChild. > > Is there something you need us ("APZ folks") to do here, or is this > something you will implement? I haven't been following the TabGroup changes. Flagging on Bill for confirming this question.

I'll need to do some initial work for this and bug 1333968. Depending on how easy it is, I might just fix them both myself. There's no need for graphics people to do anything right now though.