Add optional wxWindow parameter to wxButtonBase::GetDefaultSize()

When per-monitor DPI is used, the default button size depends on the DPI of the
display. Use the window to determine this DPI.

src/univ/button.cpp

@@ -110,7 +110,7 @@ wxButton::~wxButton()
 // ----------------------------------------------------------------------------
 
 /* static */
-wxSize wxButtonBase::GetDefaultSize()
+wxSize wxButtonBase::GetDefaultSize(wxWindow* WXUNUSED(win))
 {
     static wxSize s_sizeBtn;