Add a new GetSystemColor method to native theme.

ui/gfx/native_theme_gtk.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_gtk.h"
 
+#include <gtk/gtk.h>
+
 #include "base/basictypes.h"
+#include "base/logging.h"
+#include "ui/gfx/skia_utils_gtk.h"
 
 namespace gfx {
 
 // static
 const NativeTheme* NativeTheme::instance() {
   return NativeThemeGtk::instance();
 }
 
 // static
 const NativeThemeGtk* NativeThemeGtk::instance() {
   CR_DEFINE_STATIC_LOCAL(NativeThemeGtk, s_native_theme, ());
   return &s_native_theme;
 }
 
+SkColor NativeThemeGtk::GetSystemColor(ColorId color_id) const {
+  switch (color_id) {
+    case kDialogBackgroundColor:
+      return gfx::GdkColorToSkColor(
+                     gtk_widget_get_default_style()->bg[GTK_STATE_NORMAL]);
+    default:
+      NOTREACHED() << "Invalid color_id: " << color_id;
+      break;
+  }
+  return SkColorSetRGB(255, 0, 0);  // warning red
+}
+
 NativeThemeGtk::NativeThemeGtk() {
 }
 
 NativeThemeGtk::~NativeThemeGtk() {
 }
 
 }  // namespace gfx