Extract "Close" button creation from wxInfoBarGeneric into new function.

Such buttons may be needed in other places and it's not obvious to create
them, so add a new public wxBitmapButton::NewCloseButton() method to allow
creating them easily.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72474 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/bmpbuttn.h

@@ -25,6 +25,8 @@
     #define wxHAS_BUTTON_BITMAP
 #endif
 
+class WXDLLIMPEXP_FWD_CORE wxBitmapButton;
+
 // ----------------------------------------------------------------------------
 // wxBitmapButton: a button which shows bitmaps instead of the usual string.
 // It has different bitmaps for different states (focused/disabled/pressed)
@@ -64,6 +66,12 @@ public:
                                 validator, name);
     }
 
+    // Special creation function for a standard "Close" bitmap. It allows to
+    // simply create a close button with the image appropriate for the common
+    // platform.
+    static wxBitmapButton* NewCloseButton(wxWindow* parent, wxWindowID winid);
+
+
     // set/get the margins around the button
     virtual void SetMargins(int x, int y)
     {