Bug 995605 - [Sora][Message][MMS]Can't add the text in content when forward a media MMS r=schung

The issue is that in compose.js, "pointer-events: none" is added after it's
removed, in this case.

This patch ensures that SMIL.parse always calls the callback in an asynchronous way,
so that the caller does not have any surprise.
Merge pull request #18580 from etiennesegonzac/bug-997701-tone-player-channel

Bug 997701 - Set TonePlayer's channel when creating the audi element. r=gsvelto, rik
(cherry picked from commit 3617fa6b6e5e2e3c7a198227d27a12bca830ff0a)