In-line playing of the track doesn't pause while playing music from webbrowser at the same time

[TarotChen]

Test Environment:
$ system-image-cli -i
current build number: 228
device name: krillin
channel: ubuntu-touch/rc-proposed/bq-aquaris.en
last update: 2016-01-13 07:38:39
version version: 228
version ubuntu: 20160113
version device: 20160108-efc96d8
version custom: 20151111--36-46-vivid

Steps:
1.Go to Music Scope
2.Select a local track from My Music section and tap on its thumbnail to play it on the main view
3.Launch webbrowser from launcher
4.Visit website: www.soundcloud.com
5.Select a track and play it inside browser
6.Observe the result

Actual result:
These two songs are playing at the same time.

Expected result:
The track played at step2 should be paused if start playing the second one, only one song can be played at a time.

[Marcus Tomlinson (marcustomlinson)]

I think allowing the two sources to play concurrently is acceptable behaviour, however, in this case it becomes more an issue of how to then control each individual source from the sound indicator (As reported in bug #1534169).

As the solution to bug #1534169 directly interferes with the proposed solution in this report, I am going to mark this as a duplicate so that we can track the progress of this issue in one place.