Don't hard code white background colour in generic wxDataViewCtrl.

wxDataViewMainWindow::OnPaint() always used the white brush to erase the
control background which was wrong, change it to use the background colour of
the control.

Also add tests for setting wxDataViewCtrl foreground and background colours to
the dataview sample.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62153 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/datavgen.cpp

@@ -1656,11 +1656,9 @@ void wxDataViewMainWindow::OnPaint( wxPaintEvent &WXUNUSED(event) )
     wxAutoBufferedPaintDC dc( this );
 
 #ifdef __WXMSW__
+    dc.SetBrush(GetOwner()->GetBackgroundColour());
     dc.SetPen( *wxTRANSPARENT_PEN );
-    dc.SetBrush( wxBrush( GetBackgroundColour()) );
-    dc.SetBrush( *wxWHITE_BRUSH );
-    wxSize size( GetClientSize() );
-    dc.DrawRectangle( 0,0,size.x,size.y );
+    dc.DrawRectangle(GetClientSize());
 #endif
 
     // prepare the DC