Enables hot-tracking for overflow extension buttons in the app menu

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 "base/macros.h"
 #include "base/observer_list.h"
 #include "build/build_config.h"
@@ skipping 114 matching lines @@
 
   struct MenuCheckExtraParams {
     bool is_radio;
     // Used for the disabled state to indicate if the item is both disabled and
     // selected.
     bool is_selected;
   };
 
   struct MenuItemExtraParams {
     bool is_selected;
+    int corner_radius;
   };
 
   struct MenuListExtraParams {
     bool has_border;
     bool has_border_radius;
     int arrow_x;
     int arrow_y;
     int arrow_size;
     SkColor arrow_color;
     SkColor background_color;
@@ skipping 44 matching lines @@
     bool fill_content_area;
     bool draw_edges;
     int classic_state;  // Used on Windows when uxtheme is not available.
   };
 
   struct TrackbarExtraParams {
     bool vertical;
     int classic_state;  // Used on Windows when uxtheme is not available.
   };
 
-  union ExtraParams {
+  union NATIVE_THEME_EXPORT ExtraParams {
+    ExtraParams();
+
     ButtonExtraParams button;
     InnerSpinButtonExtraParams inner_spin;
     MenuArrowExtraParams menu_arrow;
     MenuCheckExtraParams menu_check;
     MenuItemExtraParams menu_item;
     MenuListExtraParams menu_list;
     MenuBackgroundExtraParams menu_background;
     ProgressBarExtraParams progress_bar;
     ScrollbarArrowExtraParams scrollbar_arrow;
     ScrollbarTrackExtraParams scrollbar_track;
@@ skipping 166 matching lines @@
  private:
   // Observers to notify when the native theme changes.
   base::ObserverList<NativeThemeObserver> native_theme_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeTheme);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_H_