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

include/wx/gtk/filepicker.h

@@ -105,6 +105,8 @@ public:     // overrides
     FILEDIRBTN_OVERRIDES
 
 protected:
+    virtual bool GTKShouldConnectSizeRequest() const { return false; }
+
     wxDialog *m_dialog;
 
     DECLARE_DYNAMIC_CLASS(wxFileButton)