[MacViews] Show combobox menu popup at mouse press

ui/views/style/platform_style.h

Index: ui/views/style/platform_style.h
diff --git a/ui/views/style/platform_style.h b/ui/views/style/platform_style.h
index 8534aa276355da0e534c82c363f2aa1d5f5e23c6..bca38df85395b612d7e6671a1c37205b8ff4dc29 100644
--- a/ui/views/style/platform_style.h
+++ b/ui/views/style/platform_style.h
@@ -9,6 +9,7 @@
 
 #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"
 
@@ -42,6 +43,9 @@ class VIEWS_EXPORT PlatformStyle {
   // 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