Add wxWebView::GetNativeBackend() method.

This allows to use platform-specific methods in user code.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72210 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/webview_webkit.h

@@ -114,6 +114,8 @@ public:
     virtual void RegisterHandler(wxSharedPtr<wxWebViewHandler> handler);
     virtual wxVector<wxSharedPtr<wxWebViewHandler> > GetHandlers() { return m_handlerList; }
 
+    virtual void* GetNativeBackend() const { return m_web_view; }
+
     /** TODO: check if this can be made private
      * The native control has a getter to check for busy state, but except in
      * very recent versions of webkit this getter doesn't say everything we need