Bug 1521947 - add telemetry to know what default blocking-autoplay setting users usually use. r=johannh,janerik

Add a scalar 'autoplay_default_blocked' which records a boolean value which indicates whether user is blocking autoplay by default.

Differential Revision: https://phabricator.services.mozilla.com/D17298

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

browser/components/nsBrowserGlue.js

@@ -1369,6 +1369,12 @@ BrowserGlue.prototype = {
     Services.prefs.addObserver("urlclassifier.trackingTable", this._matchCBCategory);
     Services.prefs.addObserver("network.cookie.cookieBehavior", this._matchCBCategory);
     Services.prefs.addObserver(ContentBlockingCategoriesPrefs.PREF_CB_CATEGORY, this._updateCBCategory);
+    Services.prefs.addObserver("media.autoplay.default", this._updateAutoplayPref);
+  },
+
+  _updateAutoplayPref() {
+    let blocked = Services.prefs.getIntPref("media.autoplay.default", 1);
+    Services.telemetry.scalarSet("media.autoplay_default_blocked", blocked);
   },
 
   _matchCBCategory() {

toolkit/components/telemetry/Scalars.yaml

@@ -951,6 +951,22 @@ media:
       - main
       - content
 
+  autoplay_default_blocked:
+    bug_numbers:
+      - 1521947
+    description: >
+      Whether the user blocked autoplay by default. Recorded when the preference is toggled.
+    expires: "72"
+    kind: boolean
+    notification_emails:
+      - cpearce@mozilla.com
+      - alwu@mozilla.com
+      - nohlmeier@mozilla.com
+    release_channel_collection: opt-out
+    record_in_processes:
+      - main
+      - content
+
 # The following section contains content process base counters.
 dom.contentprocess:
   buildID_mismatch: