Plumbs through support for painting the scrollbarcorner

ui/native_theme/native_theme.h

 // 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.
 
 #ifndef UI_NATIVE_THEME_NATIVE_THEME_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_H_
 
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/native_theme/native_theme_export.h"
@@ skipping 48 matching lines @@
     kScrollbarLeftArrow,
     kScrollbarRightArrow,
     kScrollbarUpArrow,
 
     kScrollbarHorizontalThumb,
     kScrollbarVerticalThumb,
     kScrollbarHorizontalTrack,
     kScrollbarVerticalTrack,
     kScrollbarHorizontalGripper,
     kScrollbarVerticalGripper,
+    // The corner is drawn when there is both a horizontal and vertical
+    // scrollbar.
+    kScrollbarCorner,
     kSliderTrack,
     kSliderThumb,
     kTabPanelBackground,
     kTextField,
     kTrackbarThumb,
     kTrackbarTrack,
     kWindowResizeGripper,
     kMaxPart,
   };
 
@@ skipping 218 matching lines @@
   unsigned int thumb_inactive_color_;
   unsigned int thumb_active_color_;
   unsigned int track_color_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeTheme);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_H_