Bug 1631957 - Clear the about:home cache on locale change. r=k88hudson

Differential Revision: https://phabricator.services.mozilla.com/D72490

browser/components/BrowserGlue.jsm

@@ -5003,6 +5003,7 @@ var AboutHomeStartupCache = {
     Services.obs.addObserver(this, "ipc:content-created");
     Services.obs.addObserver(this, "process-type-set");
     Services.obs.addObserver(this, "ipc:content-shutdown");
+    Services.obs.addObserver(this, "intl:app-locales-changed");
 
     this._cacheEntryPromise = new Promise(resolve => {
       this._cacheEntryResolver = resolve;
@@ -5046,6 +5047,7 @@ var AboutHomeStartupCache = {
     Services.obs.removeObserver(this, "ipc:content-created");
     Services.obs.removeObserver(this, "process-type-set");
     Services.obs.removeObserver(this, "ipc:content-shutdown");
+    Services.obs.removeObserver(this, "intl:app-locales-changed");
 
     if (this._cacheTask) {
       this._cacheTask.disarm();
@@ -5554,6 +5556,10 @@ var AboutHomeStartupCache = {
 
   observe(aSubject, aTopic, aData) {
     switch (aTopic) {
+      case "intl:app-locales-changed": {
+        this.clearCache();
+        break;
+      }
       case "process-type-set":
       // Intentional fall-through
       case "ipc:content-created": {

browser/components/newtab/test/browser/abouthomecache/browser.ini

@@ -14,6 +14,7 @@ prefs =
 
 [browser_basic_endtoend.js]
 [browser_bump_version.js]
+[browser_locale_change.js]
 [browser_no_cache.js]
 [browser_overwrite_cache.js]
 [browser_process_crash.js]

browser/components/newtab/test/browser/abouthomecache/browser_locale_change.js

@@ -0,0 +1,20 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Tests that the about:home startup cache is cleared if the app
+ * locale changes.
+ */
+add_task(async function test_locale_change() {
+  await BrowserTestUtils.withNewTab("about:home", async browser => {
+    await simulateRestart(browser);
+    await ensureCachedAboutHome(browser);
+
+    Services.obs.notifyObservers(null, "intl:app-locales-changed");
+
+    await simulateRestart(browser, false);
+    await ensureDynamicAboutHome(browser);
+  });
+});