Fix arrow position in action-style comboboxes on Linux in GTK theme mode.

ui/views/controls/combobox/combobox.h

Index: ui/views/controls/combobox/combobox.h
diff --git a/ui/views/controls/combobox/combobox.h b/ui/views/controls/combobox/combobox.h
index dacfbdf129016f19b9f78e69ce6bdaa005b32cd4..22781a8ab1f5d8ea4e1c0b1d80f242c08cebb398 100644
--- a/ui/views/controls/combobox/combobox.h
+++ b/ui/views/controls/combobox/combobox.h
@@ -159,6 +159,9 @@ class VIEWS_EXPORT Combobox : public MenuDelegate,
   int GetDisclosureArrowLeftPadding() const;
   int GetDisclosureArrowRightPadding() const;
 
+  // Returns the size of the disclosure arrow.
+  gfx::Size ArrowSize() const;
+
   // Handles the clicking event.
   void HandleClickEvent();