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)
Merge branch 'v1.3' into v1.3t