chromeos: convert remaining AshTest usage to AshTestBase

ash/system/update/tray_update_unittest.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 "ash/system/update/tray_update.h"
 
 #include "ash/public/interfaces/update.mojom.h"
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray.h"
 #include "ash/system/tray/system_tray_controller.h"
-#include "ash/test/ash_test.h"
+#include "ash/test/ash_test_base.h"
 #include "base/strings/utf_string_conversions.h"
 #include "ui/events/event.h"
 #include "ui/views/controls/label.h"
 
 namespace ash {
 
-using TrayUpdateTest = AshTest;
+using TrayUpdateTest = test::AshTestBase;
 
 // Tests that the update icon becomes visible when an update becomes
 // available.
 TEST_F(TrayUpdateTest, VisibilityAfterUpdate) {
   SystemTray* tray = GetPrimarySystemTray();
   TrayUpdate* tray_update = tray->tray_update();
 
   // The system starts with no update pending, so the icon isn't visible.
   EXPECT_FALSE(tray_update->tray_view()->visible());
 
@@ skipping 19 matching lines @@
 
   // Tray item is now visible.
   EXPECT_TRUE(tray_update->tray_view()->visible());
 
   tray->ShowDefaultView(BUBBLE_CREATE_NEW);
   base::string16 label = tray_update->GetLabelForTesting()->text();
   EXPECT_EQ("Restart to update Adobe Flash Player", base::UTF16ToUTF8(label));
 }
 
 }  // namespace ash