Bug 1510700 wait for ContextualIdentityService before updating Discovery cookies r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D13291

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

browser/components/nsBrowserGlue.js

@@ -1579,8 +1579,9 @@ BrowserGlue.prototype = {
    * to the other ones scheduled together.
    */
   _scheduleStartupIdleTasks() {
-    Services.tm.idleDispatchToMainThread(() => {
-      ContextualIdentityService.load();
+    Services.tm.idleDispatchToMainThread(async () => {
+      await ContextualIdentityService.load();
+      Discovery.update();
     });
 
     Services.tm.idleDispatchToMainThread(() => {
@@ -1672,10 +1673,6 @@ BrowserGlue.prototype = {
         LiveBookmarkMigrator.migrate().catch(Cu.reportError);
       });
     }
-
-    Services.tm.idleDispatchToMainThread(() => {
-      Discovery.update();
-    });
   },
 
   /**

toolkit/components/contextualidentity/ContextualIdentityService.jsm

@@ -147,7 +147,7 @@ _ContextualIdentityService.prototype = {
   },
 
   load() {
-    OS.File.read(this._path).then(bytes => {
+    return OS.File.read(this._path).then(bytes => {
       // If synchronous loading happened in the meantime, exit now.
       if (this._dataReady) {
         return;