Add wxInfoBar::RemoveButton() method.

Also change the GTK implementation to use a separate wxInfoBarGTKImpl to store
its data, this object won't be even allocated if a generic implementation is
used under GTK.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62277 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/infobar.h

@@ -44,6 +44,8 @@ public:
     virtual void AddButton(wxWindowID btnid,
                            const wxString& label = wxString());
 
+    virtual void RemoveButton(wxWindowID btnid);
+
     // implementation only
     // -------------------
 
@@ -53,9 +55,11 @@ protected:
     virtual bool GTKShouldConnectSizeRequest() const { return false; }
 
 private:
-    void Init() { m_label = NULL; }
+    void Init() { m_impl = NULL; }
 
-    GtkWidget *m_label;
+
+    // only used when the native implementation is really being used
+    class wxInfoBarGTKImpl *m_impl;
 
     wxDECLARE_NO_COPY_CLASS(wxInfoBar);
 };