[MacViews] Show combobox menu popup at mouse press

ui/views/style/platform_style.h

 // Copyright 2015 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_VIEWS_STYLE_PLATFORM_STYLE_H_
 #define UI_VIEWS_STYLE_PLATFORM_STYLE_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "ui/views/controls/button/button.h"
+#include "ui/views/controls/button/custom_button.h"
 #include "ui/views/controls/combobox/combobox.h"
 #include "ui/views/views_export.h"
 
 namespace views {
 
 class Border;
 class FocusableBorder;
 class Label;
 class LabelButton;
 class LabelButtonBorder;
@@ skipping 13 matching lines @@
   static const int kMinLabelButtonWidth;
   static const int kMinLabelButtonHeight;
 
   // Whether dialog-default buttons are given a bold font style.
   static const bool kDefaultLabelButtonHasBoldFont;
 
   // Whether dragging vertically above or below a textfield's bounds selects to
   // the left or right end of the text from the cursor, respectively.
   static const bool kTextfieldDragVerticallyDragsToEnd;
 
+  // The menu button's action to show the menu.
+  static const CustomButton::NotifyAction kMenuNotifyActivationAction;
+
   // Creates an ImageSkia containing the image to use for the combobox arrow.
   // The |is_enabled| argument is true if the control the arrow is for is
   // enabled, and false if the control is disabled. The |style| argument is the
   // style of the combobox the arrow is being drawn for.
   static gfx::ImageSkia CreateComboboxArrow(bool is_enabled,
                                             Combobox::Style style);
 
   // Creates the appropriate border for a focusable Combobox.
   static std::unique_ptr<FocusableBorder> CreateComboboxBorder();
 
@@ skipping 23 matching lines @@
   static std::unique_ptr<Border> CreateThemedLabelButtonBorder(
       LabelButton* button);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformStyle);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_STYLE_PLATFORM_STYLE_H_