Bug 1668139 - part2 : add a telemetry probe to know how many actions are handled by default handler or media session handler. r=chunmin

It would be good for us to know how many websites actually use MediaSession API to control (play/pause/stop) their media playback, an how many websites use our default handler.

Differential Revision: https://phabricator.services.mozilla.com/D93283

dom/media/mediacontrol/ContentMediaController.cpp

@@ -10,6 +10,7 @@
 #include "mozilla/dom/CanonicalBrowsingContext.h"
 #include "mozilla/dom/ContentChild.h"
 #include "mozilla/StaticPtr.h"
+#include "mozilla/Telemetry.h"
 #include "nsDataHashtable.h"
 #include "nsGlobalWindowOuter.h"
 
@@ -328,6 +329,9 @@ void ContentMediaController::HandleMediaKey(MediaControlKey aKey) {
   }
   LOG("Handle '%s' event, receiver num=%zu", ToMediaControlKeyStr(aKey),
       mReceivers.Length());
+  AccumulateCategorical(
+      mozilla::Telemetry::LABELS_MEDIA_CONTROL_HANDLE_PLAY_PAUSE_STOP_ACTIONS::
+          DefaultHandler);
   // We have default handlers for play, pause and stop.
   // https://w3c.github.io/mediasession/#ref-for-dom-mediasessionaction-play%E2%91%A3
   switch (aKey) {

dom/media/mediacontrol/ContentPlaybackController.cpp

@@ -7,6 +7,7 @@
 #include "MediaControlUtils.h"
 #include "mozilla/dom/MediaSession.h"
 #include "mozilla/dom/Navigator.h"
+#include "mozilla/Telemetry.h"
 #include "nsFocusManager.h"
 
 // avoid redefined macro in unified build
@@ -61,6 +62,14 @@ void ContentPlaybackController::NotifyMediaSession(
     LOG("Handle '%s' in media session behavior for BC %" PRIu64,
         ToMediaSessionActionStr(aDetails.mAction), mBC->Id());
     MOZ_ASSERT(session->IsActive(), "Notify inactive media session!");
+    if (aDetails.mAction == MediaSessionAction::Play ||
+        aDetails.mAction == MediaSessionAction::Pause ||
+        aDetails.mAction == MediaSessionAction::Stop) {
+      AccumulateCategorical(
+          mozilla::Telemetry::
+              LABELS_MEDIA_CONTROL_HANDLE_PLAY_PAUSE_STOP_ACTIONS::
+                  MediaSessionHandler);
+    }
     session->NotifyHandler(aDetails);
   }
 }

toolkit/components/telemetry/Histograms.json

@@ -15130,6 +15130,20 @@
     "description": "Counts the number of times users enable and use media control on different platforms.",
     "releaseChannelCollection": "opt-out"
   },
+  "MEDIA_CONTROL_HANDLE_PLAY_PAUSE_STOP_ACTIONS": {
+    "record_in_processes": ["content"],
+    "products": ["firefox"],
+    "alert_emails": [
+      "alwu@mozilla.com",
+      "cchang@mozilla.com"
+    ],
+    "bug_numbers": [1668139],
+    "expires_in_version": "90",
+    "kind": "categorical",
+    "labels": ["DefaultHandler", "MediaSessionHandler"],
+    "description": "The number of times `play/pause/stop` actions are being handled on either default handler or media session action handler.",
+    "releaseChannelCollection": "opt-out"
+  },
   "QM_QUOTA_INFO_LOAD_TIME_V0": {
     "record_in_processes": ["main"],
     "products": ["firefox", "fennec"],