Fix menu corners: the menu background was being painted as a rect when in fact,

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 117 matching lines @@
     int arrow_x;
     int arrow_y;
     SkColor background_color;
     int classic_state;  // Used on Windows when uxtheme is not available.
   };
 
   struct MenuSeparatorExtraParams {
     bool has_gutter;
   };
 
+  struct MenuBackgroundExtraParams {
+    int corner_radius;
+  };
+
   struct ProgressBarExtraParams {
     double animated_seconds;
     bool determinate;
     int value_rect_x;
     int value_rect_y;
     int value_rect_width;
     int value_rect_height;
   };
 
   struct ScrollbarArrowExtraParams {
@@ skipping 35 matching lines @@
   };
 
   union ExtraParams {
     ButtonExtraParams button;
     InnerSpinButtonExtraParams inner_spin;
     MenuArrowExtraParams menu_arrow;
     MenuCheckExtraParams menu_check;
     MenuItemExtraParams menu_item;
     MenuListExtraParams menu_list;
     MenuSeparatorExtraParams menu_separator;
+    MenuBackgroundExtraParams menu_background;
     ProgressBarExtraParams progress_bar;
     ScrollbarArrowExtraParams scrollbar_arrow;
     ScrollbarTrackExtraParams scrollbar_track;
     ScrollbarThumbExtraParams scrollbar_thumb;
     SliderExtraParams slider;
     TextFieldExtraParams text_field;
     TrackbarExtraParams trackbar;
   };
 
   // Return the size of the part.
@@ skipping 85 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_