Try to get rid of all direct references to particular native themes.

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

 // Copyright (c) 2012 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 "ui/views/widget/desktop_aura/desktop_window_tree_host_win.h"
 
 #include "base/memory/ptr_util.h"
 #include "third_party/skia/include/core/SkPath.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 89 matching lines @@
   // All HWND's we create should have WindowTreeHost instances associated with
   // them. There are exceptions like the content layer creating HWND's which
   // are not associated with WindowTreeHost instances.
   aura::WindowTreeHost* host =
       aura::WindowTreeHost::GetForAcceleratedWidget(hwnd);
   return host ? host->window()->GetProperty(kContentWindowForRootWindow) : NULL;
 }
 
 // static
 ui::NativeTheme* DesktopWindowTreeHost::GetNativeTheme(aura::Window* window) {
-  // Use NativeThemeWin for windows shown on the desktop, those not on the
-  // desktop come from Ash and get NativeThemeAura.
-  aura::WindowTreeHost* host = window ? window->GetHost() : NULL;
-  if (host) {
-    HWND host_hwnd = host->GetAcceleratedWidget();
-    if (host_hwnd &&
-        DesktopWindowTreeHostWin::GetContentWindowForHWND(host_hwnd)) {
-      return ui::NativeThemeWin::instance();
-    }
-  }
-  return ui::NativeThemeAura::instance();
+  return ui::NativeTheme::GetInstanceForNativeUi();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostWin, DesktopWindowTreeHost implementation:
 
 void DesktopWindowTreeHostWin::Init(aura::Window* content_window,
                                     const Widget::InitParams& params) {
   // TODO(beng): SetInitParams().
   content_window_ = content_window;
   wants_mouse_events_when_inactive_ = params.wants_mouse_events_when_inactive;
@@ skipping 859 matching lines @@
 
 // static
 DesktopWindowTreeHost* DesktopWindowTreeHost::Create(
     internal::NativeWidgetDelegate* native_widget_delegate,
     DesktopNativeWidgetAura* desktop_native_widget_aura) {
   return new DesktopWindowTreeHostWin(native_widget_delegate,
                                       desktop_native_widget_aura);
 }
 
 }  // namespace views