Move SetBackgroundBitmap() from wxPanel to new wxCustomBackgroundWindow.

wxCustomBackgroundWindow is a new class allowing to set a custom bitmap for
the background of any window. The relevant code was mostly moved from wxPanel
to which it was added only recently (before 2.9.2) making it unnecessary to
preserve compatibility.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69378 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/erase/erase.cpp

@@ -30,6 +30,7 @@
     #include "wx/wx.h"
 #endif
 
+#include "wx/custombgwin.h"
 #include "wx/dcbuffer.h"
 
 // ----------------------------------------------------------------------------
@@ -52,7 +53,7 @@ public:
 };
 
 
-class MyCanvas : public wxScrolledWindow
+class MyCanvas : public wxCustomBackgroundWindow<wxScrolledWindow>
 {
 public:
     MyCanvas(wxFrame *parent);
@@ -310,8 +311,9 @@ BEGIN_EVENT_TABLE(MyCanvas, wxScrolledWindow)
 END_EVENT_TABLE()
 
 MyCanvas::MyCanvas(wxFrame *parent)
-        : wxScrolledWindow(parent, wxID_ANY)
 {
+    Create(parent, wxID_ANY);
+
     m_useBuffer = false;
     m_useBgBmp = false;
     m_eraseBgInPaint = false;