Partial revert of https://codereview.chromium.org/1911973002/

ui/native_theme/native_theme_aura.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/native_theme/native_theme_aura.h"
 
 #include <limits>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 49 matching lines @@
   }
 
   NOTREACHED();
   return 0xFF;
 }
 
 const SkColor kTrackColor = SkColorSetRGB(0xF1, 0xF1, 0xF1);
 
 }  // namespace
 
-#if !defined(OS_WIN)
 // static
 NativeTheme* NativeTheme::GetInstanceForWeb() {
   return NativeThemeAura::instance();
 }
 
 // static
 NativeThemeAura* NativeThemeAura::instance() {
   CR_DEFINE_STATIC_LOCAL(NativeThemeAura, s_native_theme, ());
   return &s_native_theme;
 }
-#endif
 
 NativeThemeAura::NativeThemeAura() {
   // We don't draw scrollbar buttons.
 #if defined(OS_CHROMEOS)
   set_scrollbar_button_length(0);
 #endif
 
   // Images and alphas declarations assume the following order.
   static_assert(kDisabled == 0, "states unexpectedly changed");
   static_assert(kHovered == 1, "states unexpectedly changed");
@@ skipping 143 matching lines @@
                                            State state,
                                            const gfx::Rect& rect) const {
   // Overlay Scrollbar should never paint a scrollbar corner.
   DCHECK(!IsOverlayScrollbarEnabled());
   SkPaint paint;
   paint.setColor(SkColorSetRGB(0xDC, 0xDC, 0xDC));
   canvas->drawIRect(RectToSkIRect(rect), paint);
 }
 
 }  // namespace ui