ui: Move NativeTheme files into ui/base/native_theme/ directory.

ui/base/native_theme/native_theme.cc

 // Copyright (c) 2011 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/gfx/native_theme.h"
+#include "ui/base/native_theme/native_theme.h"
 
-#include "ui/gfx/size.h"
-
-namespace gfx {
+namespace ui {
 
 unsigned int NativeTheme::thumb_inactive_color_ = 0xeaeaea;
 unsigned int NativeTheme::thumb_active_color_ = 0xf4f4f4;
 unsigned int NativeTheme::track_color_ = 0xd3d3d3;
 
 void NativeTheme::SetScrollbarColors(unsigned inactive_color,
                                      unsigned active_color,
                                      unsigned track_color) const {
   thumb_inactive_color_ = inactive_color;
   thumb_active_color_ = active_color;
   track_color_ = track_color;
 }
 
 // NativeTheme::instance() is implemented in the platform specific source files,
 // such as native_theme_win.cc or native_theme_linux.cc
 
-}  // namespace gfx
+}  // namespace ui