Bug 1578615 - part10 : do not enable delaying autoplay during test by default. r=chunmin

Tests which use this feature on testing should enable the pref explicitly.

Differential Revision: https://phabricator.services.mozilla.com/D45756

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

browser/base/content/test/tabs/browser_multiselect_tabs_mute_unmute.js

@@ -1,4 +1,5 @@
 const PREF_MULTISELECT_TABS = "browser.tabs.multiselect";
+const PREF_DELAY_AUTOPLAY = "media.block-autoplay-until-in-foreground";
 const PAGE =
   "https://example.com/browser/browser/base/content/test/tabs/file_mediaPlayback.html";
 
@@ -19,7 +20,7 @@ async function addMediaTab() {
 
 add_task(async function setPref() {
   await SpecialPowers.pushPrefEnv({
-    set: [[PREF_MULTISELECT_TABS, true]],
+    set: [[PREF_MULTISELECT_TABS, true], [PREF_DELAY_AUTOPLAY, true]],
   });
 });
 

testing/profiles/common/user.js

@@ -62,5 +62,7 @@ user_pref("media.autoplay.enabled.user-gestures-needed", true);
 user_pref("media.autoplay.ask-permission", false);
 user_pref("media.autoplay.block-webaudio", false);
 user_pref("media.allowed-to-play.enabled", true);
+// Ensure media can always play without delay
+user_pref("media.block-autoplay-until-in-foreground", false);
 user_pref("toolkit.telemetry.coverage.endpoint.base", "http://localhost");
 user_pref("layout.css.moz-binding.content.enabled", true); // Le sad