Make wxWrapSizer demo in the layout sample more dynamic.

Allow adding checkboxes to and removing them from the wrap sizer to
demonstrate how it adjusts to its contents dynamically.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72536 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/layout/layout.h

@@ -133,6 +133,17 @@ class MyWrapSizerFrame: public wxFrame
 {
 public:
     MyWrapSizerFrame(const wxString &title, int x, int y );
+
+private:
+    void OnAddCheckbox(wxCommandEvent& event);
+    void OnRemoveCheckbox(wxCommandEvent& event);
+
+    void DoAddCheckbox();
+
+    wxWindow* m_checkboxParent;
+    wxSizer* m_wrapSizer;
+
+    DECLARE_EVENT_TABLE()
 };
 
 // controls and menu constants