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/window.h

@@ -363,6 +363,11 @@ protected:
     // should be called from OnInternalIdle() if it's overridden
     void GTKUpdateCursor();
 
+    // Return true from here if PostCreation() should connect to size_request
+    // signal: this is done by default but doesn't work for some native
+    // controls which override this function to return false
+    virtual bool GTKShouldConnectSizeRequest() const { return !IsTopLevel(); }
+
     void ConstrainSize();
 
 private: