Simplify ExtensionInstallChecker into a single-use class

extensions/test/extension_test_notification_observer.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "extensions/test/extension_test_notification_observer.h"
 
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/notification_service.h"
@@ skipping 109 matching lines @@
   content::WindowedNotificationObserver(
       NOTIFICATION_EXTENSION_PROCESS_TERMINATED,
       content::NotificationService::AllSources())
       .Wait();
   return (GetNonTerminatedExtensions(extension_id, context_) == NULL);
 }
 
 bool ExtensionTestNotificationObserver::WaitForCrxInstallerDone() {
   int before = crx_installers_done_observed_;
   WaitForNotification(NOTIFICATION_CRX_INSTALLER_DONE);
-  return crx_installers_done_observed_ == before + 1;
+  return crx_installers_done_observed_ == before + 1 &&
+         !last_loaded_extension_id_.empty();
 }
 
 void ExtensionTestNotificationObserver::Watch(
     int type,
     const content::NotificationSource& source) {
   CHECK(!observer_);
   observer_.reset(new content::WindowedNotificationObserver(type, source));
   registrar_.Add(this, type, source);
 }
 
@@ skipping 60 matching lines @@
   condition_.Reset();
   quit_closure_.Reset();
 }
 
 void ExtensionTestNotificationObserver::MaybeQuit() {
   if (condition_.Run())
     quit_closure_.Run();
 }
 
 }  // namespace extensions