Bug 1656994: Track how much longer language pack updates take than app update downloads in telemetry. r=mhowell

Uses a linear histogram with buckets of 30 seconds centred around 5 minutes.

Depends on D86273

Differential Revision: https://phabricator.services.mozilla.com/D86274

toolkit/components/telemetry/Histograms.json

@@ -6777,6 +6777,18 @@
     "description": "Update: Result code from downloading a partial update via BITS",
     "operating_systems": ["windows"]
   },
+  "UPDATE_LANGPACK_OVERTIME": {
+    "record_in_processes": ["main"],
+    "products": ["firefox"],
+    "alert_emails": ["application-update-telemetry-alerts@mozilla.com", "dtownsend@mozilla.com"],
+    "expires_in_version": "never",
+    "kind": "linear",
+    "high": 600,
+    "n_buckets": 22,
+    "releaseChannelCollection": "opt-out",
+    "bug_numbers": [1656994],
+    "description": "Update: How much longer langpacks took to download than the app update in seconds."
+  },
   "UPTAKE_REMOTE_CONTENT_RESULT_1": {
     "record_in_processes": ["all"],
     "products": ["firefox", "fennec", "thunderbird"],

toolkit/mozapps/update/UpdateService.jsm

@@ -4573,6 +4573,10 @@ Downloader.prototype = {
       })
       .finally(() => {
         this._langPackTimeout = null;
+
+        if (TelemetryStopwatch.running("UPDATE_LANGPACK_OVERTIME", update)) {
+          TelemetryStopwatch.finish("UPDATE_LANGPACK_OVERTIME", update);
+        }
       });
 
     LangPackUpdates.set(
@@ -5424,6 +5428,14 @@ Downloader.prototype = {
     // If we're still waiting on language pack updates then run a timer to time
     // out the attempt after an appropriate amount of time.
     if (this._langPackTimeout) {
+      // Start a timer to measure how much longer it takes for the language
+      // packs to stage.
+      TelemetryStopwatch.start(
+        "UPDATE_LANGPACK_OVERTIME",
+        unwrap(this._update),
+        { inSeconds: true }
+      );
+
       setTimeout(
         this._langPackTimeout,
         Services.prefs.getIntPref(

toolkit/mozapps/update/tests/unit_aus_update/languagePackUpdates.js

@@ -11,8 +11,9 @@ const { PromiseUtils } = ChromeUtils.import(
   "resource://gre/modules/PromiseUtils.jsm"
 );
 const { setTimeout } = ChromeUtils.import("resource://gre/modules/Timer.jsm");
-
-gDebugTest = true;
+const { TelemetryTestUtils } = ChromeUtils.import(
+  "resource://testing-common/TelemetryTestUtils.jsm"
+);
 
 AddonTestUtils.init(this);
 setupTestCommon();
@@ -66,6 +67,10 @@ add_task(async function init() {
 });
 
 add_task(async function testLangpackUpdateSuccess() {
+  let histogram = TelemetryTestUtils.getAndClearHistogram(
+    "UPDATE_LANGPACK_OVERTIME"
+  );
+
   let updateDownloadNotified = false;
   let notified = waitForEvent("update-downloaded").then(
     () => (updateDownloadNotified = true)
@@ -99,6 +104,14 @@ add_task(async function testLangpackUpdateSuccess() {
   resolve();
 
   await notified;
+
+  // Because we resolved the lang pack call after the download completed a value
+  // should have been recorded in telemetry.
+  let snapshot = histogram.snapshot();
+  Assert.ok(
+    !Object.values(snapshot.values).every(val => val == 0),
+    "Should have recorded a time"
+  );
 });
 
 add_task(async function testLangpackUpdateFails() {
@@ -186,6 +199,9 @@ add_task(async function testRedownload() {
   // download the complete mar. We should only call the add-ons manager to stage
   // language packs once in this case.
   Services.prefs.setBoolPref(PREF_APP_UPDATE_STAGING_ENABLED, false);
+  let histogram = TelemetryTestUtils.getAndClearHistogram(
+    "UPDATE_LANGPACK_OVERTIME"
+  );
 
   let partialPatch = getRemotePatchString({
     type: "partial",
@@ -239,6 +255,14 @@ add_task(async function testRedownload() {
 
   Assert.equal(downloadCount, 2, "Should have seen two downloads");
   Assert.equal(stageCount, 1, "Should have only tried to stage langpacks once");
+
+  // Because we resolved the lang pack call before the download completed a value
+  // should not have been recorded in telemetry.
+  let snapshot = histogram.snapshot();
+  Assert.ok(
+    Object.values(snapshot.values).every(val => val == 0),
+    "Should have recorded a time"
+  );
 });
 
 add_task(async function finish() {