Added GTKShouldConnectSizeRequest() to prevent size_request handling.

Don't hard code the exception for GtkFileChooserButton in
wxWindow::PostCreation() in wxGTK, handling size_request signal also breaks
other controls (e.g. upcoming wxInfoBar native implementation). Instead,
define a virtual function which may be overridden to return false if
size_request shouldn't be connected.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62273 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/window.cpp

@@ -2365,16 +2365,7 @@ void wxWindowGTK::PostCreation()
 #endif
     }
 
-#ifdef GTK_IS_FILE_CHOOSER_BUTTON
-    if (!gtk_check_version(2,6,0) && GTK_IS_FILE_CHOOSER_BUTTON(m_widget))
-    {
-        // If we connect to the "size_request" signal of a GtkFileChooserButton
-        // then that control won't be sized properly when placed inside sizers
-        // (this can be tested removing this elseif and running XRC or WIDGETS samples)
-        // FIXME: what should be done here ?
-    } else
-#endif
-    if ( !IsTopLevel() ) // top level windows use their own callback
+    if ( GTKShouldConnectSizeRequest() )
     {
         // This is needed if we want to add our windows into native
         // GTK controls, such as the toolbar. With this callback, the