Bug 1366808: Add telemetry probe for about:restartrequired page. r=jimm,chutten

browser/modules/ContentCrashHandlers.jsm

@@ -322,6 +322,12 @@ var TabCrashHandler = {
 
     browser.docShell.displayLoadError(Cr.NS_ERROR_BUILDID_MISMATCH, uri, null);
     tab.setAttribute("crashed", true);
+
+    // Make sure to only count once even if there are multiple windows
+    // that will all show about:restartrequired.
+    if (this._crashedTabCount == 1) {
+      Services.telemetry.scalarAdd("dom.contentprocess.buildID_mismatch", 1);
+    }
   },
 
   /**

browser/modules/test/browser/browser.ini

@@ -50,3 +50,4 @@ support-files =
   usageTelemetrySearchSuggestions.xml
 [browser_UsageTelemetry_content.js]
 [browser_UsageTelemetry_content_aboutHome.js]
+[browser_UsageTelemetry_content_aboutRestartRequired.js]

browser/modules/test/browser/browser_UsageTelemetry_content_aboutRestartRequired.js

@@ -0,0 +1,30 @@
+"use strict";
+
+const SCALAR_BUILDID_MISMATCH = "dom.contentprocess.buildID_mismatch";
+
+add_task(async function test_aboutRestartRequired() {
+  let CrashHandlers = {};
+  ChromeUtils.import("resource:///modules/ContentCrashHandlers.jsm",
+                     CrashHandlers);
+
+  // Let's reset the counts.
+  Services.telemetry.clearScalars();
+
+  let scalars =
+    getParentProcessScalars(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTOUT);
+
+  // Check preconditions
+  is(scalars[SCALAR_BUILDID_MISMATCH], undefined,
+     "Build ID mismatch count should be undefined");
+
+  // Simulate buildID mismatch
+  CrashHandlers.TabCrashHandler._crashedTabCount = 1;
+  CrashHandlers.TabCrashHandler.sendToRestartRequiredPage(
+    gBrowser.selectedTab.linkedBrowser);
+
+  scalars =
+    getParentProcessScalars(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTOUT);
+
+  is(scalars[SCALAR_BUILDID_MISMATCH], 1,
+     "Build ID mismatch count should be 1.");
+});

toolkit/components/telemetry/Scalars.yaml

@@ -776,6 +776,20 @@ dom.contentprocess:
     record_in_processes:
       - 'main'
 
+  buildID_mismatch:
+    bug_numbers:
+      - 1366808
+    description: >
+      The number of times the about:restartrequired page appeared due to a
+      buildID mismatch between the parent and the content processes.
+    expires: never
+    kind: uint
+    notification_emails:
+      - spohl@mozilla.com
+    release_channel_collection: opt-out
+    record_in_processes:
+      - 'main'
+
 devtools.toolbar.eyedropper:
   opened:
     bug_numbers: