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

ui/native_theme/native_theme_mac.mm

 // Copyright (c) 2013 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_mac.h"
 
 #import <Cocoa/Cocoa.h>
 #include <stddef.h>
 
 #include "base/mac/mac_util.h"
@@ skipping 95 matching lines @@
 }  // namespace
 
 namespace ui {
 
 // static
 NativeTheme* NativeTheme::GetInstanceForWeb() {
   return NativeThemeMac::instance();
 }
 
 // static
+NativeTheme* NativeTheme::GetInstanceForNativeUi() {
+  return NativeThemeMac::instance();
+}
+
+// static
 NativeThemeMac* NativeThemeMac::instance() {
   CR_DEFINE_STATIC_LOCAL(NativeThemeMac, s_native_theme, ());
   return &s_native_theme;
 }
 
 // static
 SkColor NativeThemeMac::ApplySystemControlTint(SkColor color) {
   if ([NSColor currentControlTint] == NSGraphiteControlTint)
     return ColorToGrayscale(color);
   return color;
@@ skipping 300 matching lines @@
   canvas->drawDRRect(outer_shape, shape, paint);
 }
 
 NativeThemeMac::NativeThemeMac() {
 }
 
 NativeThemeMac::~NativeThemeMac() {
 }
 
 }  // namespace ui