Use correct theme for the off icon of NightLight, fix tooltip and a11y

ash/system/tiles/tray_tiles_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/tiles/tray_tiles.h"
 
+#include "ash/system/night_light/night_light_toggle_button.h"
 #include "ash/system/tiles/tiles_default_view.h"
 #include "ash/system/tray/system_menu_button.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/test/test_session_controller_client.h"
 #include "components/user_manager/user_type.h"
 #include "ui/views/view.h"
 
 using views::Button;
 
 namespace ash {
@@ skipping 15 matching lines @@
   }
 
   views::CustomButton* GetSettingsButton() {
     return tray_tiles()->default_view_->settings_button_;
   }
 
   views::CustomButton* GetHelpButton() {
     return tray_tiles()->default_view_->help_button_;
   }
 
-  views::CustomButton* GetNightLightButton() {
+  NightLightToggleButton* GetNightLightButton() {
     return tray_tiles()->default_view_->night_light_button_;
   }
 
   views::CustomButton* GetLockButton() {
     return tray_tiles()->default_view_->lock_button_;
   }
 
   views::CustomButton* GetPowerButton() {
     return tray_tiles()->default_view_->power_button_;
   }
@@ skipping 63 matching lines @@
   std::unique_ptr<views::View> default_view(
       tray_tiles()->CreateDefaultViewForTesting());
   EXPECT_EQ(Button::STATE_DISABLED, GetSettingsButton()->state());
   EXPECT_EQ(Button::STATE_DISABLED, GetHelpButton()->state());
   EXPECT_EQ(Button::STATE_DISABLED, GetNightLightButton()->state());
   EXPECT_EQ(Button::STATE_DISABLED, GetLockButton()->state());
   EXPECT_EQ(Button::STATE_NORMAL, GetPowerButton()->state());
 }
 
 }  // namespace ash