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

ui/base/native_theme/native_theme_base.cc

Index: ui/base/native_theme/native_theme_base.cc
diff --git a/ui/gfx/native_theme_base.cc b/ui/base/native_theme/native_theme_base.cc
similarity index 99%
rename from ui/gfx/native_theme_base.cc
rename to ui/base/native_theme/native_theme_base.cc
index 61683822e92d053f4925d703ee0033e3ebe9621e..4f8667010c94b262098aa68a42c127160e327583 100644
--- a/ui/gfx/native_theme_base.cc
+++ b/ui/base/native_theme/native_theme_base.cc
@@ -2,7 +2,7 @@
 // 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_base.h"
+#include "ui/base/native_theme/native_theme_base.h"
 
 #include <limits>
 
@@ -51,7 +51,7 @@ SkColor BrightenColor(const color_utils::HSL& hsl, SkAlpha alpha,
 
 }  // namespace
 
-namespace gfx {
+namespace ui {
 
 gfx::Size NativeThemeBase::GetPartSize(Part part,
                                        State state,
@@ -970,4 +970,4 @@ SkColor NativeThemeBase::OutlineColor(SkScalar* hsv1, SkScalar* hsv2) const {
   return SaturateAndBrighten(hsv2, -0.2f, diff);
 }
 
-}  // namespace gfx
+}  // namespace ui