Bug 873955 - [System][Notification] Notification does not make sound when silent mode is off.
Merge pull request #9873 from alivedise/bugzilla/873955_v1-train

Bug 873955 - [System][Notification] Notification does not make sound when silent mode is off...cherry-pick from 19f77d82fb60b4d2999202a59fa84a2062bf3ea3, r=alive, a=blocking-b2g:tef+