Bug 1565689 - part3 : use static pref to control audio competing. r=baku

We don't want to enable audio competing by default, so hide this feature behind a static pref.

Differential Revision: https://phabricator.services.mozilla.com/D38143

--HG--
extra : moz-landing-system : lando

dom/media/mediacontrol/AudioFocusManager.cpp

@@ -7,6 +7,7 @@
 #include "MediaControlService.h"
 
 #include "mozilla/Logging.h"
+#include "mozilla/StaticPrefs_media.h"
 
 extern mozilla::LazyLogModule gMediaControlLog;
 
@@ -41,6 +42,12 @@ void AudioFocusManager::RevokeAudioFocus(uint64_t aId) {
 }
 
 void AudioFocusManager::HandleAudioCompetition(uint64_t aId) {
+  // Enable audio focus management will start the audio competition which is
+  // only allowing one controller playing at a time.
+  if (!StaticPrefs::media_audioFocus_management()) {
+    return;
+  }
+
   for (size_t idx = 0; idx < mOwningFocusControllers.Length(); idx++) {
     const uint64_t controllerId = mOwningFocusControllers[idx];
     if (controllerId != aId) {

modules/libpref/init/StaticPrefList.yaml

@@ -5353,6 +5353,11 @@
   value: false
   mirror: always
 
+- name: media.audioFocus.management
+  type: bool
+  value: false
+  mirror: always
+
 #---------------------------------------------------------------------------
 # Prefs starting with "mousewheel."
 #---------------------------------------------------------------------------